Team composition is going to depend heavily if you are using offense or defense and specifically if you are talking about arena, TW, or Grand arena.
GA-Defense: Bastila lead, old Ben, Ezra, 2x Jedi and then you save JKR for offense with an undermanned squad. Or you set JKR on offense and you want the typical arena/meta squad because you're going against someone with the same or better mods. TW you're talking about basically the full metal/arena squad unless you have 10-12 g12+ Jedi with a ton of good mods.
Padme needs c3p0 but that's for offense. Having CLS and 4 legendary/Journey characters is really cheesy to me especially when you have JTR, JKR, or Padme wanting some of them. CLS, Han, Chewie, R2 is the typically set. Again, GA, not a full squad and you save one elsewhere. Usually I'll toss a Phoenix for a 5th just to get another rebel tank or attacker.
Saying what the "best" is, that's very subjective, but we can discuss it and break it down. Asking what is best for your specific situation, well, it really depends on a lot of factors and we simply don't have the data needed to offer the advice you'd want.