Hi Scarcrow & welcome to GW!
I loved playing GW1 for many reasons, but one of the big ones was because of how it's set up in terms of being an MMO. It isn't like WoW, where there are other people around both in towns and out in the explorable zones... it's an instanced game. An MMO in town, but more like an organized co-op once you go out into the explorable areas: you create a party with other players in town and then venture out together into areas in which you and the other members of your party are the only players.
For some (like me) this is a plus... for diehard MMO players, it's a big change and potentially a negative.
I've been playing GW2 during the BWEs now... it's set up like a more traiditional MMO where it's a persistent, wide-open world that other people are playing in. But what's lovely about it is that there is no kill stealing, no loot stealing, no griefing, etc. GW1 and GW2 are two very
different games in many, many ways... but both are (in my opinion) simply fabulous.
So it's really going to depend on what you expect from your MMOs. If you're looking for more of a WoW-like experience (persistent, open world with thousands of other people), you're probably going to like GW2 better. If you like the idea of having an instanced world where the only people in the explorable areas are those you've chosen to be there with, you'll like GW1.
Last thought: the population in GW1 has decreased drastically. Unless you join a guild, it may be hard to find people to play with. The game offers henchmen (right away) and heroes (earned through progression) to accompany you instead of humans if need be, so the low population won't stop you from playing - and finishing - the game. It just may not offer the "social" atmosphere as much as it once did.
It's still an awesome game though, especially for the price (and no subscription!) and would be a good time-killer until next month when GW2 officially launches. Plus, if you get the EotN expansion, you can earn some nice little rewards for use in GW2!