For an interactive and generally (usually) more interesting pet, I recommend lizards. (Though I haven't kept geckos.. So I may be wrong in assuming they're as friendly and interactive as my beardie.)
For an easy to care for animal that doesn't need to be fussed about, snakes win hands down.
It's all in what you prefer. I've come to prefer some interaction from my pet... It's the same reason I'm a dog person rather than a cat person. The legged reptiles tend to be more interactive ("engaging," as David put it), so they appeal to me more. As people have said, though, they ARE more work. Much more work.
Even with Leopard geckos.. If almost everyone who's posted is right, you're talking about feeding every day or two, and cleaning poo just as often. Even if Nate is right, and the care is as easy as that of a corn snake, you're still looking at maintaining a supply of live insect feeders (compared to simply stashing a bag of mice in the freezer like you would for a snake). Those insects can be a deal-breaker for many people.
The right snake can be an interesting, interactive pet, too. They just aren't usually as "aware" of you as a lizard is. Though a gecko or bearded dragon will interact with you, and register that you are a large, living creature, the average snake will either fear you or view as nothing more than a warm tree that supplies it with food on a regular basis.
The ultimate decision of which one is the best pet ultimately falls on YOU. What is the best pet for myself, or for any other poster here, may not necessarily be the best pet for you. We have given you the pros, the cons, our opinions, and our reasons for what we prefer; now it's up to you to decide which animal most appeals to your own preferences.