Both are better, if you can level them both to 50. :D
Right now, Thm is considered the most powerful class for end-game stuff like NMs. They're the only class of which I'm aware that can actually solo NMs. Their huge cone-shaped AoE makes them the best healers; their DoT spells do not scale down on high level mobs, so they can do (by far) the most damage per second on NMs (plus, Shadowsear is a killer); and they've even got Emulate, which makes them effective as tanks (!!). But, as in everything else, the actual answer depends on what you enjoy doing most.
As for the OP, the advice I've been giving to friends is, the game is still undergoing huge changes. They're adding content every month. So if you can wait a few more months, the game will have more content, and the content that's there will be more polished.
That's not to say that it's unplayable now. Far from it. I've been playing since CE, I've been enjoying it. And the game has absolutely gotten better. And, of course, we'd love to have you join those of us still playing. :D But I'd hate to have you come back and the game hasn't changed quite enough to keep you around. We want you in for the long haul.
If you do come back, then if I may be so bold, a couple pieces of advice:
1) Join a linkshell as quickly as possible. That way, you'll have people to socialize with, people to party with, people who can help you out, and people who can offer advice if you need it.
2) When choosing your starting city, I'd suggest starting in Uldah, or getting there as soon as you can. Most of the players have migrated to Uldah, so it's the best place to find other people to interact with, and the market wards have by far the most goods for sale.
Good luck!
