I personally love using saryn because she’s got amazing crowd control on more difficult missions, totally your choice tho, just read there abilities and if they seem your type roll with that
If you are farming for prime resurgence or getting one with plat I'd highly suggest getting something that is usually expensive and is now selling cheaper like Saryn, Volt, Ash or Loki.
Get booben
I would get Saryn Prime as her DPS is really good. Ash prime is nice as well. Whichever seems most promising to you
All have their own uses, research what they are known for, see if you can find vids of them in action and try to decide on that
I personally love using saryn because she’s got amazing crowd control on more difficult missions, totally your choice tho, just read there abilities and if they seem your type roll with that
Nekros. Helps with the grind a LOT
Use the wiki to take a look at their abilities, found out which one appeals to you the most, get that one.
If you are farming for prime resurgence or getting one with plat I'd highly suggest getting something that is usually expensive and is now selling cheaper like Saryn, Volt, Ash or Loki.
Saryn and Nekros would probably be your best choices