Honestly I find the engineers in general kinda boring, but I’d probably go with proxy just cause I like fast squishy mercs.
Fletcher is my second, he’s still pretty fast, but his weapons are kinda eh. Never been a fan of shotguns, and the blish always feels weird to me on him, despite maining blish on aura. Plus his stickies still feel clunky. Too many buttons to use them since I’m more used to using abilities with the number keys rather than the quick selection buttons, and stickies still frequently disappear when switching to the detonator too early, even though they’ve pretty much already left your hand.
Bush is my third, he’s not bad, but his weapons are pretty generic so he’s nothing special to play as. The turret being a hands off ability as well doesn’t help that. Not really a big fan of the turret in general either, how it still glows even after you’ve destroyed it, or how you can reclaim it once it’s been destroyed but only if it doesn’t magically fall through the floor. Or hell, just how boring and static it is to fight against. Ultimately he’s pretty boring to play as and fight against imo, and it doesn’t help now that there are so many clueless new players playing him.
Turtle is probably my least favourite. He’s basically the same as bush, same boring character, weapons and ability, a meh personality, etc. His shield’s deploy time is so high that it makes it pretty unsatisfying to use, and then once it is up it usually only takes a few seconds for someone to land a grenade behind it and leave you with a massive cooldown. Never been a big fan of shields in PVP games either though, they usually feel pretty out of place, especially in a fast game like dirty bomb