I bought Guild Wars: Factions about a year ago, and it bored the shit out of me. I gave up playing a week later.
I bought Guild Wars: Prophecies a month ago, and I loved it! However, leveling up went slow and walking around in the barren ashes of what used to be Ascalon and it's surrounding provinces doesn't suit me... also, fighthing Charr became boring quite soon...
I bought Guild Wars: Nightfall two days ago and I'm LOVING IT!!! Dervish is the most interesting, and most cool-looking class I've ever seen in ANY mmo, you level up quite quickly, you get lots of information and trainings right away at the start of the game, and you also get Heroes, which are like AI-controlled characters you can completely control. Also the main enemy seems to be Corsairs, which are african-looking pirates really, but I can tell you that I always prefer fighting humanoid creatures over beast-or plant-creatures. Also, the environment in Nightfall is absolutely beautiful, walking around in a lusch (sp?) jungle really beats the Prophecies areas..
Guild Wars: Eye of the North is an expansion pack that fits with all three main campaigns, but you can only play it if you already have a level 20 character. So I would not recommend you buy that just yet, I haven't got it myself either.
I would recommend you purchase Nightfall, because my farvorites are:
#1: Guild Wars: Nightfall
#2: Guild Wars: Prophecies
#3: Guild Wars: Factions
Good luck!
