I keep my beardie's temps so that the hottest spot is about 105 and the lowest temperature on the basking site is 90-95. He'll bask around a lot, and hibernate through winter, but they really enjoy getting heated up under the basking lamp and then coming out to run around and get into trouble.
I would like to get a tegu though when I move out. Right now I have a beardie and a mali uro (recently rescued from a very neglectful owner...he had her in a ten gallon tank with nothing but a hot rock, old food, a rock, a disgusting water dish, and tons of feces...there's a lot about it around the uro forum). I barely have enough space for the beardie's enclosure and the enclosure I am soon to get for the Uro (she's in a 29 gallon right now). That's something you should take into consideration too. Tegus definately need a lot of space, and their enclosures are usually more utilitarian. If you want a reptile that you can play with but who's enclosure can be designed to look almost like fine furniture, a beardie is the way to go. Only problem with that way of keeping a beardie is that you don't want to feed them crickets in the tank (if you use anything other than carpet or shelf liner), and it's a little more upkeep to make it look nice.
There's really a lot of variables. A beardie usually comes pre tamed (just the way they are I guess), but a tegu will take time to tame down. An adult tegu is an impressive site though. I'd say go with your whichever one will be better suited to your life, and which ever one your instincts tell you to go with.
-ryan
