I changed your pic to a link.. since that's not your picture, you can't post it directly.. always link to a pic that isn't yours.

Savannahs can get 4-5' long too and are going to need at LEAST a 6' cage when full grown, if not an 8' cage. Since you are young, I would definitely say an ackie! Awesome lizards, and they won't get too big on you like a sav can. Excellent start for monitors, and are pretty easy to breed too if that's what you're interested in.