Your "Dream Team"

Mages:

Wynne because she has a level hea and is a good healer for the team.

Bethany because like Wynne she's quite a caring person but at same time she's probnably more adept with more offensive magic than Wynne.

Dorian for the lolz really and the fact that like Bethany he's more familiar with offensive spells.

Rogues:

Got to have my 2 favouriet DA characters wit hme whic hare both rogues which are Leliana and Varric.

Leliana I like because of her versatility and adaptability a sshe seems to b ejust as deadly with daggers in her hands as she is with a bow and I've always valued versatility.

Varric well you can't go wrong with his trusty Bianca also most of DA2's finest moments come through him so he's on my team for that.

Isabella would probably be my 3rd rogue to add some variety her dualist skills can make her quite deadly when she puts her mind to it. She may be a pirate by nature but she can have a heart of gold when it matters.

Warriors:

Alistair Can' t go wrong with his Majesty the King of Ferelden He makes for a pretty decent tank option and hi stempla rskills are very useful at nullifying magic.

Cassandra Well someones go ttto keep our littl e dwarf in check but honestly like Alistair she's a fantastic tank with templar skills and rarely goes down in my playthroughs.

My final party member would probably be Iron Bull mostly because I find him a decent 2 handed warrior and being able to use bigger 2 handed weapons will add some versatility.

Assuming they're all based on what they are by 9:44 (so essentially a DA4 dream team) but not dead, I'd go for:
Warrior: Blackwall, Oghren, Sten
Rougue: Cole, Sebastian, Nathaniel "Mo-fo'ing" Howe
Mage: Morrigan, Merrill, Finn (from Witch Hunt)

Morrigan and Merill is a meeting I'd like to see, especially if it's to go up against Solas and possible the Evanuris.
If I had 2 mage slots free I'd have picked Anders and Vivienne for another meeting I'd love to see.

Warriors: Alistair, Aveline, Sten
Rogues: Isabela, Leliana, Varric
Mages: Morrigan, Vivienne, Merrill

My dream team would be

Sera - Rogue
Dorian - Mage
Iron Bull - Warrior

i don't care if another team would be better in combat i just want to have fun along the way and those three together are fun.

That last phrase, explanation "why" in this way is simple, short and at the same time gives exact explanation (reminded me of Sera tbh, one of th best charactrs in DAU).
Great.

Warriors: Oghren, Alistair, Bull
Mages: Dorian, Anders(Awakening), Merrill
Rogues: Sera, Zevran, Isabela

Just because that seems like a team that would get into a lot of trouble

I'd just really like to know what the banter would look like if you stuff Anders and Vivienne in a team together.

The Arishok and Ser Cauthrien would be the ideal dream team.

In term of badasserie and gameplay skill set from the trilogy anyway.
The Arishok have 2 handed weapon on each hands and Cauthrien has literally better stats than the Archdemon.

Nuff said.

Warriors - Alistair, Fenris, Blackwall
Mages - Morrigan, Merrill, Dorian
Rogues - Zevran, Isabela, Sera

Honorable mentions:

Warriors - Iron Bull
Mages - Velanna
Rogues - Cole

I picked these guys because many of them are my favorite characters, not because I think they'd make a good team in combat. Now, putting together a dream team of companions based on skill or who would have the best banter would be interesting... but I'd have to put some thought into that. Maybe another time.