Wow, I can't believe how people hijacked this thread to talk about little girls running around in bikinis.
I've played both Tera and GW2 (beta weekend) and their combat is kind of the same. Almost. Only Tera has the very same mechanics as "all the other" MMO's where you get your 50 skills and all you have to worry about is which number to press first, second, third etc.
But of course, they have their "combo" which gives it a new touch, even though you could just press that skill (or any other) anyway - you don't get any bonus damage, cooldown or whatnot for using the "combo". Just an easier way to macro without actually using macros.
Guild Wars 2, on the other hand, has a personal story that differs from race and profession, it's better active combat (in my opinion) and it's way to get people to play together, not against each other like people most likely are used to.
GW2's cross-profession combos are pretty cool (although not awesome) where you could put up a field of fire and I'd shoot my regular arrows through it, making my arrows ignite and *poof*, I've got fire arrows also damaging the enemy over time, on top of their regular damage.
There are lots and lots of other combos you can make, but you'll have to look that up yourself if you're interested.
For me, Tera is just like all the other MMO's, but with better combat and a political system that seems like a fun idea.
Guild Wars 2 has done a good enough overhaul of most game mechanics of the regular MMO and made them better in a way that makes it feel new and fresh. Also, there is way less grinding, the dynamic group events (much like Rift, only better thought out and great) and the way the game doesn't get you to hate all people outside your party is just great.
Both games are great, but in my opinion, Guild Wars 2 seems to be the better game. Although it's not out yet, so you could always play Tera now and go for GW2 whenever it gets released.
Oh, and knowing ArenaNet the updates won't be few, they will be plenty and often, and mostly based on their community.