Hi. Honestly I wouldn't suggest starting with either if this is you first lizard, but between the two options I would go with the rock monitor. A healthy iguana will start having hormonal issues that can make them go from happy cute lizard to raging scaled demon for a few months out of the year, especially if you end up with a male. Also, both animals require massive caging relative to what you are used to with snakes, so bear that in mind as well.