I think I'm just going to wing it based on personalities, with adjustments made for character-specific quests or the like. At first I tried to spend some time with each companion in DAII, but I ended up really disliking some, finding others just "meh" (Fenris, I'm looking at you), and then typically going with the comedic-relief trinity (Aveline, Isabela, Merrill) or, if I could manage having three rogues (including Hawke), occasionally Varric in place of Aveline.
From the videos it looks like we're pretty much going to have to travel with some version of the trinity here, just for exploration purposes: warriors are needed to bash in walls/doors, rogues to pick locks, and mages to reconstruct collapsed bridges. I don't mind it in theory, but I'm crossing my fingers that I'll actually like a mage and a warrior rather than having to put up with them. (I'm going rogue.
)
Just for fun, here's some math, inspired by the comment in one of the recent ads that there are over a hundred potential party combos:
Total possible combinations with a free choice of any of the 9 companions, unrestricted by class (explanations under the spoilers -- please correct my math if I'm wrong!):
9 * 8 * 7 = 504
<-- mind blown
For those who want to cover the two non-PC classes, the number is a little more manageable:
3 * 3 * 7 = 63
And finally for those who want the trinity covered by their companions:
3 * 3 * 3 = 27
So it seems like there are plenty of options at least numbers-wise.
Do we know yet if there will be an approval system and if so how it will work? I recall that being a big consideration party-wise in DA:O (and in DAII until I got all of the companions locked in).