I mix it up so much that I tend to have lots of different teams, rather than one 'standard'. I tend to take Solas around with me a lot given his tendency to drop lore bombs that I've initially missed - otherwise, it's pretty flexible.
The Classic Team: Cassandra, Varric, Solas. Oh c'mon, they're all great, they all have some of my favourite dialogue.
The Fun Team: Iron Bull, Sera, Blackwall/Dorian interchangeably, depending if I want to hear more great Sera dialogue or more Adoribull.
The Team That Is Most Likely to Burn the Winter Palace Down With Every Noble Inside: Sera, Solas, and Blackwall. Sometimes exchange with Iron Bull if I need a little more chill in my team - Qun!Bull totally would though, if only during an invasion.
The Least Faves (aka I feel bad for not taking this group out enough): Vivienne, Cole, and Dorian/Varric. I actively feel guilty about how much I neglect Vivienne given how tanky and beautiful and snarky she is.
Finally, if I've decided I no longer give any fucks: Solas, Vivienne, Dorian + Mage!Quisitor. Endless barriers, endless fire mines, endless snark. I took this group on my last run through the Temple of Mythal (five mages, if you include Morrigan) and it was glorious. Given the amount of barrier spamming and AOE spells that goes on it's quite easy to do this for the whole game on lower dififculties, but then again, I play mage almost exclusively and I have a much better handle on how they work together.