I hope you're not saying the quests are better in Guild Wars? I found it to be annoyingly repetitive, NEVER visually interesting, and frequently very difficult to find the objectives on a map. I hated the cutscenes. In-game cutscenes looked cheesy, are boring to watch, and never got me excited/interested in the story.
co-operative pve play is boring and tedious, and I rarely felt like I had a great time with a team working hard together. The combat was SOOO boring, but that might have been even worse because I chose a rogue as my first character and all I seemed to be able to accomplish was firing arrows.
I also found the system for learning new skills (finding particular trainers hiding all over the place to get particular skills), to be insanely annoying. The best skills are all given by people hidden away somewhere way off the beaten path (in places I could not find without help), or had to actually be stolen of monsters?? So, the concept is to only give those high end skills to experienced players who already know where to go and what to do? that sure makes for some fair PVP for newcomers.
GW = a quick 20 levels of character building, followed by endless PVP.
WoW = a LOT more character building, MUCH easier to understand gear stats, and often visually interesting instances (giant stone statue bosses, huge dragons, castles with narrow halls and interesting lighting, etc).
I love PVE instancing and co-op play. Maybe that's why I prefer WoW so much. I don't feel the need to prove myself to anyone, but would rather help others and have a good time. PVP seems to be full of disrespectful people with poor sportsmanship (spitting on killed victims, laughing at them, etc). That is not to say ALL PVPers are like that, but I have come accross many (in both games) who are arrogant and self-important.