im having a hard time deciding between Elementialist, mez, or ranger
Ele is awesome damage with a rather unique weapon/skill set combo. (each weapon set essentially has 20 skills tied to it, depending on elemental attunement that you are using. You can't switch weapons during fight, but you can switch between 4 attunements.)
I've heard great things about ranger, at least--it is very different from GW1. I haven't tried one, so I can't say much about it. At the very least, the sound effect for the rain of arrows skill or whatever is absolutely terrifying if you're nearby.
i love mes so that's what I'm going with. The class seems to have undergone the most nerfing/buffing of all of them (mostly nerfing) to this point. It's a very odd playstyle. You do need to remain on the periphery most of the time, and casting through allies to hit your targets. there are some up close skills, but you utilize them by jumping in, popping a clone or phantasm, and getting the fuck out. there is a damage mitigation phantasm that is quite useful for more up close play, but it only get you so far.
Ele is the squishiest of the bunch. I forgot to mention that it also lays down various walls and traps that are used as combos for allies (fire wall--ranger can stand behind this and shoot arrows towards target--arrows become fire arrows, etc)