I play Mercenary as Hybrid spec Bodyguard/Arsenal and i made this videos:
Mercenary Hybrid video 1
Mercenary Hybrid Video 2
i Think this is the best build for a mercenary in PVP, you can make good damange, and have a good survive. Also you can help to the group to take position in bases. I do easy near 200 K Dmg and 200k heal in each warzone.
More videos of PVP, PVE and bosses here in my Mercenary Channel