Personally I am a big fan of blue tongues and have kept a bunch of them for many years. I have one large male that has been with me 16 years and he was almost this large when I got him so its quite possible he is over 20 years old and still going strong and breeding like a teenager.
Of course Im biased but I find them to be delightful lizards. Most of mine are tame to the point that I would have to pester one to get it to bite. They dont mind handling, although they dont love it. They tend to be a little more wiggly then say a bearded dragon which will just sit in your hand. But they arent aggresive. I do have one rogue though that will snap. Thats rare though.
Their diet is simple and their care is not complicated. They do not require a tremendous time commitment. Provided they have ample heat, food, clean water and hiding places they should do just fine.
Intelligence? I do not find them to be as inquisitive about their surroundings as say a monitor. They spend a lot of time hiding although they do come out and explore a bit.
Captive bred babies are readily available.
Those are the pros. The cons? Not many. They arent the most active lizards in the world. They have short stumpy legs so if you want a lot of action they may not be for you. And they will not tolerate handling quite as well as some other species.
A savannah would be a fine choice but bear in mind they do become quite large, require huge amounts of food and while most become quite docile they are capeable of delivering a painful bite if they are so inclined. They are quite intelligent as far as lizards go. Lets face it, none of them are rocket scientists. A good choice but not my personal pick as I find them dull and messy. Personally if I was going to get a smaller species. More expensive, but more interesting MHO.
I have never had a frilled dragon. Some friends of mine have and from what I have been told they can be a little more delicate and require a bit more care than some of the other species on your list.
Blue tegus are gorgeous and similar to a monitors in many ways. They get big, they eat a lot and they can bite. Personally I have found tegus to be agressive but others have told me they can become quite tame. Could be a good choice. Maybe not the best choice though.
As another poster mentioned a bearded dragon might be your best bet. Attractive, readily available, easy to keep, docile. They dont get as large as some of the others but certainly arent tiny. Quite active little guys, too.
Id go with either a blue tongue (bias, I know) or a bearded. Dont think you would be unhappy with either species.