well to me i can chooose 3 types of moniters. 1. a ackie 2. a green tree 3. peach throat. One i may not recommend is a savannah moniter. unless you have moniter experince these animals have been known to be quite strong and inflict pain full bites.
well basically it depends on you would you like a aboreal looking moniter or a ground dewelling.

personally i like a green tree cause they come in attractive colors such as green, blue and what not. but these terffic moniters are still hard to find and can be from$200-500+.