Mercenary: A5 barb, cap attack speed (speedcalc), +all skills, physical resistance, Sharkbaiter, high dps sword,Bogspitter
That is general.
For ultimate GG merc I'd go something like:
weapon: grandfather (match ias to not hit 100% ds penalty)
gloves: krys for slow
belt: one of belts with 10% slow (endless loop or black void)
chest: razorspine for spikenova procs
helm: str craft for more spieknova procs
amulet: rare with banish
boots: str craft
Something like this can clear fauzt/vizjun solo on almost any build