There is a huge difference between the two concerning their care. Most geckos are very hardy and easy to care for. The opposite applies for most Chameleons.
I have a Panther Chameleon, a Fat Tailed Gecko and six Leopard Geckos. Four of the Leopards are juvenile and I bred them myself. The Geckos basicly need access to a bowl of water and crickets at least every couple of days and a source of heat. They would be quite comfortable in something as simple as a shoebox with something for them to hide in.
My Chameleon needs so much more. He must be misted in the morning and evenings to provide drinking water. Chameleons do not drink from a water dish, they drink drops of water off the plant leaves in their enclosure. This misting also serves to raise the humidity in the Chameleons area. Most Chameleons require quite a bit of humidity, but they also need very good ventilation or they can develop respiratory infections. Most people keep the larger Chameleons in screen enclosures for the purpose of good ventilation. Chameleons are diurnal rather the nocturnal like most Geckos so the Chameleon needs UV lights in addition to heat lamps for basking. They also easily bore of the same type of insects and so a variety of insects is necessary to keep the Chameleon happy.
All in all the Geckos are much more common, easier to care for, inexpensive and longer lived of the two, but this is just a generalisation. I enjoy keeping both, but the Cameleon is much harder.
Baby Panther Chameleon (Furcifer Pardalis)
Baby Leopard Gecko (Eublepharis Macularius)