The clones are a lot of fun together. The squad of 5 is what I still use for the rancor and I've been cruising through most GW nodes for a month or so with Cody, Echo, Rex, Sarge, and Ayla. I tend to switch in plo over ayla during GW when I actually need more than a single dispel - and having two TM boosts is certainly fun too hah.
As Baze mentioned, Rex and Fives are your best bets for getting started. They are great characters in every aspect of the game - with or without other clones so you really can't go wrong and certainly won't have regrets. I also am still running a pvp squad with Rex and Fives lol so they definitely make the cut there.
Cody and Echo are still sort of lost when it comes to pvp unfortunately. Cody is one of the squishiest characters in the game and both his and Echo's assist abilities have some of the largest damage penalties in the game. They are a blast in GW, rancor, and P2/4 in AAT but they are going to continue to ride the bench in pvp with the way the meta is right now.
If you decide to get the squad you should start the grind for Sarge lol. He is the hardest hitting clone by almost twice the damage and his AOE turn meter reduction is fantastic.