Since this is all I've been playing recently...
I love Nader. I don't really have as much of a handle on the grenade arc as I would like, but I've blown up snipers and loits of people huddled around healing stations, squirrely proxies and lots and lots of turrets anyway. Martyrdom (suicide when downed) is great too. People try still try to knife you when you're down and if they're quick they can pull it off, but if not - boom. I got three people at once with that one time, it was glorious. Also she screams "Granaten!" every now and then.

Bushwhacker is nice too. His turret is pretty fragile, but if you know where to place it it can survive for quite a while and even pick off the odd fool not quick enough to duck into cover. Nice for both defense and offense, i.e. you aggro people then retreat in your mechanical friend's direction. Bushwhacker can also get what I think is the best SMG, the Kek-10 (these names

). It's really accurate and the clip is endless/the rate of fire is just right. Bushwhacker is a really nice alternative to Proxy, if you like to be the objective monkey.
I've also had the chance to try out Execution mode, which is a bit like CS. You have one life and try to advance through a map. Each section has different objectives and your team only advances to the next set if they complete them. It is a bit of a shit show though, because medics exist. You only need to kill someone once for the enemy team to be permanently weakend for the duration of the round, so if you have more or more competent medics on your team and at least one guy to give you ammo, you can simply outlast the enemy. The other modes can be pretty one-sides as well, and this mode only amplifies it.
Still having a lot of fun with this, though I mostly log off as soon as my daily missions are completed.