It is best to use UTH because belly heat helps with digestion. But, if you have too much humidity a heat lamp may be the way to go because they really zap the humidity. Either way, you still would need a thermostat, just to be on the safe side, you dont want to burn your little friend.

As for me, I have both. I use a 60 watt red heat bulb, on 24/7. I also have a UTH that is on a lamp dimmer, so the hot spot is at 89-92*F. I would just use the UTH, but I really need the heat lamp to get the ambient up to 85*F. (Keep in mind I am using a 20 gal long aquarium, so it is pretty hard to keep the right temps, but I manage).

Hope this helps,