Losse: The first one in the party. Like will I get different responses from NPCs? Or if I have different party memebers talk to NPCs do I get different responses?
IWD1?
If you're talking to a merchant, then yes, as your CHA will affect prices (you can always just select the character with the highest CHA to talk to the merchant though).
As far as other NPCs, there are a handful of occasions where it makes a difference who talks to the NPC (some convo options open up, depending on the class of the character). I think there are only one or two though that are triggered conversations where the NPC is scripted to talk to the party leader. In most other cases, you can choose any character you want to do the talking and trigger the convo yourself. Of course, this presupposes that you know which NPCs have the extra options, so you can select accordinhly.
Off the top of my head, there are extra options in convos for Bard, Paladin, Druid, and Cleric.