Probably Jack will get the majority of votes, simply because he is middle ground between rarity and usefulness.
Maui is awful, needs an astonishing amount of work before he gets good. It’s currently pretty hard to come by his chips.
Shank is purchasable and can be gained from guild crates, and is pretty powerful. Ridiculous amount of armor and good damage.
Jack is a very squishy unit that does a bit of everything except normal damage (lol). Whole team stun, two scares, healing, a good amount of aoe. And can be acquired in Heist shop, but apart from that - you can only depend on luck.