Dosu. He has Unyielding, which is a legendary ability since it was part of what made Tobi so OP back in the day.

On a serious note though:

Ukon/Sakon, since they have the pretty rare ability to attack four times (though they need someone like Bee to enable them unfortunately)

Fu Yamanaka, he has an interesting kit. Heard somewhere that he gets a skillbook that makes his puppet more like Chikushodo's Panda, except still with the chaos ability.

Edo Tensei Deidara as well, his ability set synergizes really nicely and I like how it all just fits together like a puzzle.

Tendo's a fun character as well.