Well, if you plan to bring your game into BG2, then from a story perspective it would make sense to play with the 'canon party' if you're playing good. Not at all necessary, but the game assumes that's who you played with and dialogues are structured accordingly, so you may get slightly more out of it if you pick Imoen, Minsc, Dynaheir, Khalid and Jahiera.

The NPCs in BG1 are...what you make of them, really. The game won't generally have conversations between the characters scripted out, but you can imagine and roleplay conversations between them as you wish. From that perspective, picking whichever characters you like the personalities of might be a good idea. Branwen...has a reasonably in depth backstory which does actually tie in with some early elements of the plot, so you mightl ike to keep her around for long enough to at least get back at the person who cast flesh to stone on her. You can certainly delay picking up Dynaheir until a bit after that, too, so you'll have a good idea as to whether or not you like her character by that point.

Coran I'm not familiar with. I know you said you didn't want power gaming advice, but I will say that if you dual class Imoen at level 7 or so, she can easily bring two of her four thief skills up enough to not have to worry about another thief doing it for the rest of the game (and BG2). Since pickpocket is useless, and both open locks and stealth have spells which perform the same jobs if you only plan to use them occasionally, you don't need a second thief. You will, however, want a thief while you're dual classing her, as she'll lose her abilities for a while. Since that's also when you enter the part of the game where thief abilities are more important, it's a real pain not to have one. Again, you can pick up Coran during that time if you decide to take someone else for the rest of the time, and decide if you want to continue adventuring with him. Just be careful: I have a feeling that if you choose the wrong options regarding doing his quest when you meet him, he may leave forever, so check first. You may also want to use a save editor to give him xp on a par with the rest of the party, to reduce frustration. If you do take Coran, just bear in mind that you'll only have one character who's really designed to be a tank: Minsc. Branwen, Coran and, to a lesser extent, you can do in a pinch, but aren't ideal. Also, you should probably know at this point that Black Isle rather weakened the druid class in BG2, partly by making the jump in xp needed to go from 14th to 15th level extremely high. It's still playable, but just be warned that you'll be rather weak in the late game. (Just so you know, that isn't the case in Icewind Dale, where it's a pretty strong class throughout the game. IWD2 and PS:T use different rules regarding classes, so the question is largely irrelevent for different reasons).

Either way, though, it's really up to you who you choose to adventure with, so pick characters you like. That said, if you want to take Montaron and not Xzar then you'll have to cause Xzar to die from massive damage (that is, raise dead won't work and his portrait disappears), or use one of a few exploits in the game to make Montaron 'forget' about Xzar.