Circle Tower: Wynne (obvious reasons) is the only character that has a true reason to be there. Everyone else I would think to be uninterested. I doubt Alistair would want to go back, considering how he's glad he was able to quit being a templar; however, it does kinda fit for him to be there. I sometimes take Shale along because of his dialogue, and I think it important that he gain more information on mages, considering his only experience so far has been with Wilhelm. My suggestion: Wynne, Shale, Morrigan/Alistair
Orzammar: Oghren (again, obvious reasons) and Shale definitely have ties to this, while most of the other members are largely indifferent from an RP standpoint. I would think Morrigan would object to most of the quest, since you're doing the work for someone else; this goes against her views of survival and not relying on others. Sten shares a lot of the values that the dwarven society holds. My suggestion: Oghren, Shale, Sten (though I'd definitely brew up lots of health poultices before doing this, seeing as you're lacking a healer)
Redcliffe/Urn: Alistair seems a must from an RP perspective, considering his ties to Eamon. For the Redcliffe portion, the only other character that might fall somewhat into a story purpose of being there would be Wynne (for recognizing Jowan, and later on having purpose there regarding Connor and the Circle). As for the Urn quest, you'll want a religious party, so that decision should be obvious. My suggestion: Alistair, Wynne, Leliana (just make sure you don't defile the ashes)
Brecelian Forest: From metagame knowledge, we're aware that Leliana has a desire to know more about the Dalish, so it kinda makes sense to drag her along. Zevran, being an elf himself, also could fit in (that, and from his gifts it would appear that his mother was Dalish). I would think Morrigan and Sten would object to being a part of mediating the dispute between the elves and werewolves, and I doubt Oghren would care (though the trees' canopy might provide a "roof", making him feel more at home =p ). You could probably tie Wynne into the situation, though I'm surprised she has no lines regarding how the werewolf curse has its roots in blood magic. Considering Dog doesn't really have an RP reason to be anywhere except following the PC around, I'll make the case for him to be included in this party, purely for the reason that there are loads of trees to mark his territory on (and what mabari wouldn't like to brag to his kin that he's marked a sylvan?) My suggestion: Leliana, Zevran, Dog/Wynne (again, if you take Dog, make sure you have lots of health poultices)
As for DLC locations, it would make sense for Alistair and Wynne to be included in Return to Ostagar for obvious reasons (they were there the first time), as well as at Warden's Keep (Alistair b/c he's a GW, and Wynne for the location's relationship to the Veil and blood magic). Since my suggestions involve Shale at both the Circle Tower and Orzammar, it would warrant a trip to Honnleath fairly early, so I'd suggest Alistair (due to the presence of darkspawn overrunning the place; as many GWs as possible seems appropriate), Wynne and/or Morrigan due to the presence of a demon and how Wilhelm was a mage, and perhaps Leliana, for the purposes of helping the townspeople.