In my experience with Vista, I really didn't like how they treated you like an idiot. But I never used it first hand, it was always fixing problems for people who didn't know the first thing about customizing, so it's possible you could make it feel like a big boy OS instead of a toddler toy.

I think Vista SP1 is set to hit soon, which is the landmark I know a lot of tech enthusiasts were waiting for before taking the plunge into a change over. Maybe see if a friend has it, or go to a tech store and play around on their demo computers with Vista and see what you think of the interface. I don't think bugginess is going to be a problem. It's going to come more down to personal preference.

However, I'd advise against 2000. Even though it is probably the most secure OS that Microsoft has ever released, it's quickly becoming obsolete. I know people will rip me for saying that, but really, I'd lean towards looking either solely at XP or Vista. And, between those, it'll come down to how you like your interface and how much you care about the "features" that Vista has.