I think Bushwacker rotation is the most ridiculous, imo he’s the easiest merc of them all to play. KEK-10 is amazing with tons of ammo and his special ability is fire and forget anyway, and autoaims, no need to maintain it. Can we take out turrets? Sure, i took out many, but by the time you take out 2 turrets and/or engineers, the others respawned and have placed new ones, and taking out turrets while engineers spam their 45 bullet magazine super accurate smg on you too, is not easy 
When i got friends starting Dirty Bomb, i always suggest bushwacker as the easiest Merc
Fletcher week was nothing, He takes way more skill to play so there were barely any good ones, that said, if it’s not fletcher week, i never see anyone play Fletcher but myself. Fletcher falls in the same category as Kira/Arty imo, he’s slightly outclassed or takes WAY more effort to be good with.
Phantom week: no problem, despite what people say, Phantom is really easy to counter and he’s situational, on many maps or parts of maps he’s of no real use or would contribute WAY better as another merc, ESPECIALLY vs more experienced players, which btw, was already the case pre-nerf.
Fragger week: now this is very annoying, imo fragger’s still the best overall assault, his oneshots are the real deal
A team with 3+ medics is also very annoying to play against.
Like people said: games with too many of the same class are a weakness in Dirty Bomb atm. Maybe there should be limits.
Suave