What choice do you regret most?

Not saving the Krogan Scouts but the Salarian Pathfinder instead. I don't regret saving Reeka but I wanted the Krogan to get something for once. Will be doing that in my next playthrough.
Also not something I necessarily regret but making Morda a representative (diplomat, or whatever it was called) at the end is probably a really bad choice. But again, I just really want the Krogan to have a chance and be equal and how can they grow when no one is ever giving them a chance? I just wouldn't pick Morda out of all the Krogan. Also bonus points for pissing Tann off. But a better choice would probably be the Moshae.
I don't remember any other difficult choices to be honest... Oh yeah! Saving that emotionally unstable PMS-ing Angaran AI. Jeeeesus she's too much.

Well at least your not a complete monster then.

What kill code?

Sleeping with Reyes as Sara.

My sis-Ryder was mostly a goody two shoes, and her character arc would have been better with a feeling of betrayal despite the grudging belief of Reyes as being 'better.'

I'm surprised to read how many killed Akksul. The first time he's discussed, Jaal says that Akksul will make you want to kill him. I considered this to maybe mean that Akksul would bait me, down the road. Then, just before you encounter Akksul, Jaal emphasizes that you must not interfere, no matter what happens. I trusted Jaal to handle the chump.

I think that "R2", or whatever on PC, is too much for some to resist! As I mentioned before, I impulsively killed Kalinda. Though I now feel it was a good choice, my post mission response was foolish. This time, when it's calculated, my response will reflect as much.

I've started making some alternate decisions in my NG+. The creepy, emotional AI went to the angara, this time. SAM suggested that it is angara, so I wanted them to have it. (I suspect it's more jardaan than angara; maybe even a fully formed personality. It seems so unimpressed by everyone and everything. Scary.)

One small decision I made differently involved the injured turian with an asari friend, found on Nexus Operations deck. I misunderstood the extent and nature of his trauma, last time, and told him "Eos is still dangerous". This time, I told him he could return to Eos. I expected that he would, but he's still moping, exactly as if I shut him down, again. Bugged?