I have all 6 bounty hunters 7 star (though I haven't geared Greedo), and in general, the one you want to leave out is Dengar. Unless you're facing a team with Tenacity Up all the time, he doesn't really contribute to the BH team.
Greedo and Zam are the fuel that makes Bounty Hunters go fast. Firstly Bounty Hunters gain 15% tm whenever a TD explodes. Both of them have AoE TDs. Secondly, Zam explodes TDs with her basic which gives her 100% tm.
Put together, this means that Zam and Greedo, drop their AoE TDs. Zam goes through and blows up 2 TDs on each enemy in addition to her basic attack's damage, plus gives the entire bounty hunter team a net gain of 150% tm. It's a ridiculous combo.