Well, your account has all the tools to beat everything.

You have healer BSBs & Shout. Thus, you'll likely need to RW Wall for the higher-end stuff (like I do). But you have good debuff stuff (Shelke BSB, Agrias SB, etc). Generally speaking, this is what I would center your team around.

A hastega & faith/boostga. This means Ramza for a physical team, or Serah for a mage team (looking through it quickly). Ramza can provide breakdowns as well; you only need him to be using Shout (his BSB isn't nearly as strong as Shout is). Serah can be a damage dealer with black magic & witch ability.

A healer. Eiko, Ysh, or Aerith fit that for me, mainly because BSBs allow you to go without having to hone a lot. But Alphinaud, Vanille, etc can also fit it.

A pure debuffer. For you, I'd look at Shelke or Faris, but especially Shelke. Between the two, you can have Pentabreak / Fullbreakdown / all 3 attack stats + def or res breakdown. Pretty strong. Irvine could also work here, but I don't think his stuff is as good as Shelke or Faris. But, if you prefer him, it'd definitely still work. Same with Mustadio.

That leaves 2 spots. You can either turtle up & bring a second healer (Alphinaud is especially good at this, because his SSB - Deployment Tactics - is basically a DPS on its own), or bring two DPS. I personally prefer a 2nd healer, but it's completely up to you. Finally, your DPS. This should fit the element. However, in all honesty, the DPS is the least important of your 4 slots. The healer / hastega / debuffer is more important.

In terms of DPS, I see several really good choices for you. Vincent can fit both physical & magic. With him, you'd wrath up to two SB bars, then use USB/BSB/whichever cmd fits the team. Delita would hit strong in combination with Eiko's BSB. Refia is another superb physical DPS. WoL, Yuffie, Fang, etc would all work for their elements as well. IMO, though, your top two are Vincent & Refia.

Mage-wise, Rapha, Maria, & Alphinaud are all outstanding. Again, Vincent works for both (very well). Garnet is also a good choice (Garnet BSB2 & Rapha go VERY well together).

As an example, lemme craft a physical team for you.

1) Ramza, with Mako Might or Dr. Mog's Teaching. Use Shout only. 2) Eiko, with BSB & cure/proshellga. Provides crit chance boost. 3) Shelke. Between her & Ramza, make sure all of the major debuffs are covered. (She has Magic / Mind in her BSB). 4) Vincent, with Ace Striker / Battleforged & Wrath / Dark Bargain. Wrath up to two SB gauges, use Dark Bargain, then USB, then BSB, the cmd1 until BSB runs out. Repeat.

The last person is up to your preference. But IMO...

5a) Alphinaud, with Dr. Mog's / Mako Might, using all heals (Curaga / Proshellga). 5b) Refia, with Lifesiphon to prepare for BSB spam.

I'd be happy to give more details if you'd like, but this is generally how a team should be built for most content.