I know you're going to hate me for saying this, but I have a really annoying suggestion. Play all of the classes suggested in this thread (and perhaps those that AREN'T), with the following in mind:
- You'll be playing this character for a LONG time. Choose a char you can stick with for a while.
- You probably don't want to veer too far in the direction of either Too Defensive or Too Offensive.
- Find a char that can fill a number of roles (i.e., very defensive either Protection or Healing or whatnot, and very offensive, i.e. spike/debuff). The beauty of GW lies in that most if not all characters can fit these roles.
- Don't be afraid to go for account-wide titles, such as Luxon/Kurzick, Wisdom, or the like. I'd strongly advise against going for account-wide PvP titles, since unless you're REALLY good, they're generally not worth the time. The Wisdom title in particular is relatively easy to farm, and you can work on it with other chars if you get tired of your GWAMM.
- Once you find a char that you like, find a general-purpose build for it that you can use for most stuff (like vanqing, missions, mapping, and skill capping)
I have three GWAMM Sandwiches so far (Monk, Sin, Ranger), and am closing in on my fourth (Necro). Unfortunately, I can't judge which of these was "easiest", as A) I've gotten gotten "better" at GWing, and B) the first two GWAMMs came with account-wide titles that effectively mean #3 and #4 have had significantly FEWER than 30 titles to GWAMM. That being said, Ranger was probably the easiest, as rangers are ridiculously durable (most of the high-end endgame damage is elemental, afaik, which they're resilient against).
As Gabs88 said, I'd avoid paragon. I'd disagree that monk is bad - I found monk to be perfectly fine - but paragon is as of now sorta limited in the potential really good builds it can run. Yes, Imbagon (which means basically 100 extra armor and 35% dmg reduction) can be nice, but it can get rather boring being locked into one build.