I haven't played in months..but when I played, Guitar was about as cookie cutter as it got.
Staff being second.
BUT, maniac is the shiz. Retired on a level 112 maniac (which was a couple months before the new level cap)
So as far as I remember..
If you're going pvp, you want alot of stun. And Idk if it's still useful but DMF was SUPER cookie choppin in PvP
In PvE, you want a nice amount of AoE/Support
Gunners are pretty useless here, Gunner/Inventor, Jannisary is good because of damage
Staff's damage is insane PvE, can clear things your level in 1 attack basicallly..(scud/flame blow? I think were names of the skills) but it makes you out level your guys, but best way to rush to maniac if you want (I wanted maniac, went staff, my staff hit 100 my mercs were in their 80's.)
You basically NEED a monk.
Healer is not needed but recommended, I went without one tho so it's not that hard.
Archers are good because of silence.
Vikings are great for the freeze skill.
Spearman can be nice for the AP drain but 90% of the time it takes a more experienced player to use it properly.
Swordsman are good tanks, most people get 2 until they are higher level then they get an LK.
The beast trainer quest is a pain in the ass, and very annoying. But worth getting. (Great merc)
Witch is a good merc however just like staff main she kills fast, out leveling other mercs.
Cannon guy you can get at level 20 something isn't really worth getting IMO.
When you get high enough for the good mercs, such as spartan, elementalist, etc you'll know enough to know what you need.
Also, Exo and prophet are great PvE mercs, Exo being an almost required PvP merc as well
Again: this was months ago that I played, I'm sure I can't be that out of date tho. Esp not for low levels. =]
At low levels make sure to get about +3 gear (not spirit tho) so you can skip gear sets and have no problem leveling, for instance...
Get +3 Ocean gear and skip rakasha, then get +3 assassin and skip whatever is after that..
If possible get +3 bloodknight and you can keep that until Dragon (I did with NO problem at all.)
Or you can wait on getting the nice sets (bloodknight/gilgamesh/w.e is after that...)
Wait for gilgamesh, and use gilga until Conquer, however gilga is a bit expensive (or was, rather.)
Hope this is enough to get you started. If you decide to play thebes I'm selling gold there for FG ;]