If You Had To Cut 3 Squadmates from ME2...

Mordin could be cut as a squadmate and just have him stay on the Normandy for his countermeasure against the seeker swarm

Here's my #1 reason to not cut Kasumi: she's the only person that can get Shepard out of those stupid Cerberus togs. I'm sorry, but Shepard might not even be willingly working with Cerberus (depends on your RP) so sticking them in Cerberus clothes is wrong. Kasumi's dlc offers me another option.

He's also the weakest squadmate of the twelve. I'm not saying get rid of him. I'm just saying his talent lies more with finding a way to help stop the collectors, which he does with the countermeasure against the swarms, than being a squadmate.  I already chose the three to cut. If I were to choose more, he would be one I would cut as well.

Hard to chose. I wouldn't really want to cut any of them, but I suppose we need to see who is really redundant.

Grunt - He doesn't hardly teach us anything at all about Krogan or the genophage. More damning is that he has almost no combat role due to poor powers.

Thane - Main issue is that nothing really happens with the Drell. He is sort of a more interesting version of ME1 Codex Tali, but the problem is that the Drell's tie-in are the Hanar, and they aren't remotely as important as the Geth in ME1. On the other hand, he has a good power set (bonus notwithstanding).

Jacob - I guess he is the relatively upstanding Alliance guy who joined Cerberus. I don't know that this is necessary given that hero Shepard is more or less the same except doesn't necessarily join willingly. That spot is really also taken by Chakwas, Joker, Gabby and Ken so... His role is largely pull-bot and two other characters also fill this.

Zaeed - I like Zaeed, but random merc or bounty hunter isn't necessarily needed. Maybe if the plot was different and he was involved in helping track down some of the dossier people, it would be different. Also Garrus as a vigilante isn't drastically different. Maybe merging Jacob and Zaeed would have worked. His power set is average to below average depending on how much you care about squad disruptor (so below average for me).

Morinth - she isn't actually Samara and it seems somewhat pointless that you can recruit her.

Borderline:

Samara - at least we have a more ruthless asari than the table-dancing-tarts and diplomats we mostly dealt with prior to this. But really her Justicar thing is a bit self contained and it almost seems like we get more insight into the Asari listening to the ads on Illium. Justicar also somewhat overlaps with bounty-hunter / vigilante roles of Zaeed and Garrus. Power set is above average.

Jack - We already know about Cerberus experiments, so I suppose the point is to humanize it more. She is sort of the mirror-universe Miranda in a way though. Power set is similar to Samara and Jacob (pull-bot).

Kasumi - We don't really learn much about non-alliance humans from her. She is just a thief that we can recruit, even if she is likeable. Powerset is good though, which balances that to an extent.

Garrus - I wouldn't actually drop him from the story, but he doesn't bring a whole lot of insight into any group this time around. Maybe if he had more conversations talking about how the Terminus is different than Council space or something. Power set is above average though.

The rest I think are fairly integral to different stories:

Miranda - think this is fairly obvious, but clearly you need a Cerberus cheerleader.

Tali - Synthetic-Organic conflict gets explored further in this game, and we also get to learn a bit more about the Migrant Fleet and its politics.

Legion - the other side of the above coin, and now we also get to see that Geth aren't just generic kill-bots.

Mordin - He is the response to ME1 Wrex, we learn a lot more about the genophage.

The biggest issues with both Thane and Kasumi is that you recruit an Assassin and a master thief..... whom are neither used to assassinate or steal anything. Which is unfortunately part of the greater issue of recruiting the squadmates to begin with, as other than Mordin, there's no compelling reason to really be trying to recruit these people whatsoever, as Shep/Cerberus have zero idea what's on the other end of the O4 Relay(could be a collector armada on the other side for all they know) and that some of them are indeed useful for something in the SM is a case of plot contrivance/self-fulfilling prophecy than actual foresight on the part of TIM or Shep.

Yeah, I agree and thought that Shepard should perhaps be recruiting mercenary leaders from around the galaxy rather than just always killing them.  Aria should have definitely been recruit-able.  Also, I think it would have been cool if only half of the squad mates available were names provided by TIM... e.g. they could have had one available from each of Shepard's backgrounds (ie. X old friend would show up only if Shepard had X applicable background).  They could have arranged it such that, if recruited, that old friend would always die during the SM... so it wouldn't even had to have been something they carried over into ME3.

Sorry, I take slight issue to this.

Yes, she starts off confident, sure of herself, calm and collected. She is a capable woman with a high-ranking position within Cerberus who also has a reputation for being coldly efficient, an "Ice Queen", hiding insecurities behind a facade of steely togetherness. A perfectly normal and common trait that exists in many people, burying our fears and emotions behind a well constructed illusion of being in control. Her development and story concern slowly unravelling these layers and understanding Miranda more through her troubled relationship with her father. She shows fear and concern for her sister Oriana, and her father finding her. She is concerned about Shepard, questioning him at the start, but can slowly begin to be influenced and or impressed by his leadership and even be motivated into leaving Cerberus. She expresses doubts about the success of their mission. Worry for the colonists being abducted. All of this is realised and understandable and not out of line with her arc and how she is developed through ME2. None of that seems like a devolving into someone unsure of herself. She has doubts, conflicted feelings given her origins and history. They existed at the beginning though, we just didn't know they were there. It's called character development for a reason. Yes, she complains about aspects of her life, but it is more complex than just complaining about how good she is. You take any ME character and look at them through a fundamental lense you can summarise them basically and simply, but I'd argue most of the cast, Miranda especially are much deeper than that. We are entitled to our own opinions of the characters. But our bias shouldn't ignore the development and arcs of the characters. There is more to most, if we choose not to brush over it. 

Anyways, as to the OP and poll.

For me it would be Jacob, Zaeed and Jack.

I find it difficult I think to dislike Jacob. He's easily likeable. But I've always felt given their loyalty quests, and given Miranda is better fleshed out and developed than Jacob, the two could easily have been condensed to one character. After you start recruiting, Jacob is easily forgotten. I understand why. But he is more function than character. We needed another squad mate at the beginning to accompany Shepard and Miranda. But in novel to film or to adaptations you see a lot of excess characters condensed down into one or two, and for me Jacob fits the bill of a character that could have been cut out and it wouldn't impact the game. His handling in ME3 was also the worst out of the ME2 cast for me.

Zaeed's a fun and jaded character, likeable, but flat and archetypal. His character begins and ends with his loyalty mission, one of a vengeance we can't really get behind because of Zaeed's actions on Zorya and his motivations. 

Jack for for me simply because her biotic prowess in cutscenes didn't translate to gameplay, and I felt she was much better fleshed out in ME3. Unromanced, her anger and rage don't add anything, she stays very much the same in ME2. A shame because she vastly improved for me in ME3. But with Samara later recruited, I made little use of her.

And while Kasumi suffered from being a DLC option, I can't imagine ME2 without her. Forget her being a thief, her wit was such a morale booster for me and refreshing release from some of the more serious aspects of ME2. 

I actually quite like Jacob's loyalty mission. It's not the best, but I don't mind it. Reminds me of Lord of the Flies.
Although the continuity errors are quite annoying. Ten year old thermal clips, anyone?

#1 has to be Jacob.... he just has a flat-line personality. #2 and I really hate to say this, ==== Zaeed. To me, he was the least interesting character in the whole bunch ( Jacobs backstory was kinda interesting) and of course, I really loved Zaeed's ferno nades. . RIP Robin Sachs.

The way female Shepard sounds every time she talks to him, even if the player never tried to flirt with the character.

He's a Cerberus operative on a Cerberus ship. The last time I check, ME2 didn't let Shepard steal the ship out of its factory and airlock all the Cerberus crew to rejoin the Alliance. Kinda dumb to start ME2 with just only Miranda on the ship unless you prefer Kai Leng as a squadmate.

A gif reaction?

Really?