I like tegus, though they are not monitors. The only reptiles I've owned are a beardie, savannah monitor and 3 tegus. I don't have the savy anymore, I had to find him a new home when I moved. The landlord wouldn't let me keep all of my big lizards. I still have my 3 tegus though. I love them to pieces. They're awesome.
IMO, since savys tend to be wild caught they are more moody and cautious than tegus. I'm not saying its that way for all but from the ones I've been around they're more cautious of people.
Caiman lizards are pretty cool, there are a couple people on tegutalk.com that have those and from what I've read they tend to be a little nippy but they are gorgeous. They don't get as large as tegus do but they spend more time in the water. It might be more expensive to build an enclosure that can hold water like that, unless you use a giant cat litter pan or something.
I like all of the reptiles I've had. My beardie was my first then I got into the larger lizards. I would not house any of them together if they're a different species. Some people house tegus together, 2 of mine are smaller and they're sharing an enclosure but its not a permanent plan. If you get multiple of any animal you should make sure that if need be, you have the space and money to provide a second enclosure in case of a fight or if you end up with opposite sexes.
Another smaller monitor would be an ackie. There are also blue tongued skinks.
I would choose tegus over and over. They match what I'm looking for in a reptile/pet. A savy or a tegu will require an 8x4x4 enclosure, if you house 2 together it will need to be larger. I have my enclosures stacked on top of each other. My tegus are semi-expensive to feed, they eat ground turkey, rats, eggs, chicken, fish, etc. Its more expensive than feeding crickets to a beardie but as adults they will brumate for up to 5-6 months year, during that time they don't need to eat. As adults tegus don't need to eat daily. One of mine has recently started eating every other day.
Generally tegus are not recommended for beginners, they require specific humidity levels. They also require large housing, "expensive" food and get to be a decent size. That being said, the only reptile I had before my tegus was a beardie, lol. I didn't have much experience before my tegus and I feel I'm doing a great job caring for them.
Cuban rock iguanas are cool, I'd be interested in getting one down the road when I'm older and have my own house.
If you're interested in a tegu go to thetegu.com or tegutalk.com, a lot of those members also have various monitors, iguanas and other reptiles. They can give you more info. and help you figure out what it is you want and help you figure out how to care for them properly.