World of Warcraft or 3.5? Or rather, Story vs. World?

I'm going to be running a campaign this fall with some classmates of mine. I have both the core rulebooks for Dungeons and Dragons 3.5e and the World of Warcraft RPG, and I've come to a dilema that I can't seem to solve. I'm a pretty big Warcraft fan, so I'm very knowledgable about the lore and backstory. As such, I'm very confident in my ability to tell a good story in the Warcraft universe. However, I'd also kind of like to just create a sandbox and have my players run around in it. That's something that I don't really want to do in the Warcraft universe, but rather a world that I completely create. This dilema of story vs. world, structure vs. sandbox, has really been gnawing at me over the past few weeks and I just can't seem to make a decision. I'd like feedback on this subject along with feedback from anyone who has played the WoW RPG.