Im in the same boat as you, I have a 35 merc and a 35 PT.
Gonna lvl one of them and mainly play pvp, while lvling I like playing my merc, but like everyone says they can easily be interrupted, tho I read that mercs are getting some love in patch 2.7
Ive been watching some merc pvp videos, and if mercs are left alone they can blow ppl up, but depends on your playing against I guess, someone with half a brain will try and stop the burst.
Are PT's strong in pvp????
Ive been playing some pyro mid lvl pvp on mine, I just feel a bit meh.