Do you want an animal that will become the essence of the word "dog tame"? Be fairly easy to tame? Tolerate all of your beginner mistakes with little fuss? Eat EVERYTHING you put in front of it?
Get a tegu.
The only complaints I have gotten about tegus is that they can become extremely food aggressive. Well cared for tegus are some of the most entertaining and well mannered large lizards you can own. When people get frustrated dealing with the temperament of their properly cared for monitor, I tell them to get a tegu.
They do still need lots of room to move around in, as well as a thick layer of substrate to burrow in, and have distinct humidity needs to shed properly, but compared to a monitor (tegus and monitors are not the same animals!) it may be an easier and more rewarding large lizard. I'm partial to the blues but all three of the "argentine" varieties are going to be similar as far as temperament.
They will literally eat anything you put in the cage if they're kept correctly.
It all boils down to what you want temperament wise from your 4-5' long lizard. A Savannah Monitor is going to be a challenge; a potentially very rewarding challenge, but you are going to have to put a lot in and possibly have an animal that really wants nothing to do with you. It'll be healthy, beautiful, and aloof.
Tegus have been documented in South America begging off of picnic tables for scraps. They seem to enjoy interaction, and I've encountered several that will come up to seek out your attention. One that I see regularly likes to climb into laps and get stroked. He will literally walk out of his cage, stroll around a bit, and then walk over and plop into your lap.
Either way, do lots of homework, and get the book Robyn recommended. It's a useful resource. 
~jenny
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"We call them dumb animals, and so they are, for they cannot tell us how they feel, but they do not suffer less because they have no words."
- Anna Sewell (1820-1878)