What do you think we need more of? I want to play one or the other. more of a offtank role than a backline guy

Mercenary anytime, harder, stronger, faster.
Dps, slam, det 5, cheap purge

The reply from Connavar lists pros/cons in this thread: http://www.uthgard.net/forum/viewtopic.php?f=99&t=36103

I'm too undecided yet, arms may be an option as well if you want to be able to slam/peel as well (with merc it's harder, you have to switch shield per drag&drop).

If you're just interested in playing offensively, then probably Merc is the better option!

If you want to play an armsman offensively, you are going to be frustrated a lot of the time, there are two reasons for this: PBT and Guard/Block

The big hits from pole sound great, but Pulsing blade turn really counters the slow attacks (not that too many groups will run wardens but you may come across supp RM's a bit). Block is the other big problem, against a decent guard/peeler you will suffer a lot of blocks, block seemed OP on uthgard 1 too, not sure if they changed any of the mechanics there (except defence penetration of course) Dual wield gets to half the block chance, which on top of def pen, is going to make it far easier to hit guarded targets.

If you want to play defensively/peel then arms will be far easier to do this job.

If you have a merc peeling in your 8v8 your already bound to fail. So i'd recommend not having a merc on peeling duty.
And moreover it is few and far between when you have a mid group running pbt, and same with hibs running wardens specced into pbt. I'm not saying you wont run into those type of groups but the chances are extremely rare. I wouldn't suggest speccing or building your merc for a peeler, go full dps and do what your good at. Let the armsman do what they do slam and anytime snare.