Hmmm. What's the origin roster?
Wyll, Gale, Lae'Zel, Shadowheart, Astarion.. I'd say five is a perfect compromise. You can bring the whole gang playing as one of these or bench one if you bring Tav.

I'd bench Wyll. Warlocks, I just don't get them.

Fear my wrath, for it is great indeed.