The best starter monitor is a Ackie, yes they do cost alot more than a Savannah, but they stay smaller and are far more tracktable than a Sav. Sav's also have more problems than some of the captive bred monitors as 99.9% of all savs are WC. If you are looking for a larger but not giant monitor (waters/crocs) the Argus/Sand cross's are nice I have one that is now around 22" and is about a year old. He is a killer eater and after some work on my part is not to bad to handle (so long as he isnt hungry)
Things to keep in mind with a monitor, other than Ackies they will require a large enclosure, are not going to be docile by nature(if it is its sick and ready to die), they eat alot my argus is doing 2 adult mice every 3 days, full grown he will be on rats 2 times a week. One the upside if you are prepared for the challenge of keeping one they are impressive animals are can be very entertaining to watch. Also check your local laws as many area's have past laws against keeping Large "dangerous" animals and many times monitors fall under that catagory.