Out of the Prophecies professions, my Elementalist, Ranger, Warrior, and Necromancer have seen the most play. The commentary really isn't that complete, but it should be a start.
Read a bit on the professions to choose what you want. Personally, I think that the Elementalist or Warrior are probably the easiest starting classes.
E - The sheer firepower makes things easier, particularly since it makes a bigger difference if you're running around with henchmen. Cynn isn't particularly strong.
W - The tank is usually pretty straightforward. You'd usually be expected to be in the front line soaking up damage, but there's enough space to deal some damage too.
R - You really have to appreciate utility and being able interrupt. Rangers also have many choices in what they can do, probably more than the others, since they can take advantage of
Expertise.
N - I'm not sure how to describe it. It can be pretty amusing, though. I'm not sure that it'd be as fun for a first time player, since it was my first character, but I enjoyed it more as time went on.
Mesmer - This is probably one of the harder classes to play when first starting out. It (usually) isn't as direct (role it plays) as other classes, so people often don't notice the effects. If you try to find a group, Mesmers usually aren't sought out that often. Also, the Mesmer skills in Prophecies seem a bit lacking at times. If you eventually get Factions and/or Nightfall, though, there are fun skills there.
Monk - It can get pretty boring (for me, at least) when you're usually expected to heal/protect. It's sometimes fun, but it's never been as fun for me as the others. It can be nice for farming, but when you're first starting out, that really shouldn't be the main focus.