I'm kind of in agreement with post #2. Cats, dogs and lizards are totally different in every conceivable way (except having 4 legs, a head and a tail). If you're an animal lover you would instinctively know which you have an affinity with. If you don't, you are maybe not suited to caring for any of them. Like Mike, I'm not trying to be mean. But for the animal's welfare, you need to understand what you are looking for in an animal, and what your motivations are. If it's ownership, or curiosity, or novelty, step away.
If you want a loyal friend who gets excited just to see you, you'll want a dog. But can you get the right breed for your routine, or family circumstances? Some dogs are better than others with kids. Some will get bored while you're at work and tear your house up. If you like creatures who know their own mind and who get up to all sorts of funny stuff, can be affectionate and entertaining but are basically a) mercenary and b) independent, that's a cat. If you want something that gives no emotional engagement whatsoever, and can be displayed in a cage, but occasionally attempts to rule over Mankind according to David Icke and his chums, well, there's yer lizard.