Top arena squads?

It depends on what you want out of the game. If you want to play to be like everyone else and climb in the arena easily, then get Dooku/Old Ben, QGJ, Rey, RG, and GS. Your team will be meta and look like everyone else and you will probably be able to beat most teams.

However, if you want to build a thematic team, don't be afraid to be different. You can be successful with a Rebel, droid, Jedi, or Ewok team too (oh, and clones if you are willing to pay for it). People might "target" your team in the arena because you are different, but at least you will have made a team that you want, not what everyone told you to make.

Whatever you do, make sure you decide early on and then commit to focusing on building that team instead of collecting, leveling, and gearing too many characters. It's not Pokemon, you don't have to catch them all.

As for me, I run Anakin (L), Qui-Gonn Jin, Ima-Gun Di, Yoda, and Old Ben...all F2P and I am in the top ten in my arena, hitting the top two for three of the last five days. So don't let people tell you that you can't run "so and so" team. I committed to Jedi early on and put all my resources on them (always had the 21 day pack of crystals), getting ahead of the competition on my shard by being focused on that team.