I would say that the water monitor is my favourite kind of monitor. It is probably my favourite reptile. I have one at the moment which is about 2ft long.
I have seen some very tame ones and seen some really crazy ones too but I have read that generally they can become quite tame with time and work.
With that being said I don't think most people have the ability to keep such a large lizard (it can grow 6 to 8ft in length and is a very bulky animal. Only the Komodo dragon is bigger than the water monitor). A full grown water monitor needs a room sized enclosure not a glass coffin for a slow death. I am getting a 12ft by 7ft room built in the basement of my new home for my salvator and I think this is about minimum size. The animal needs to be able to move about, dig, soak and climb. A happy animal is a healthy animal. Then you have to think about the cost of food and the cost of making one room in your house a tropical temperature. You also have to think about providing a large enough water container (pond) for a 6 to 8ft monitor to soak in. Think about cleaning poop out of a large pond and changing the water.
If you think you can house such a large animal and give it all that it needs then go for it... they are amazing animals

If not then go for something smaller like a savannah (you should give a 4ft savannah about 8ft by 4ft or space).
The more expensive (and smaller monitors) like Ackies and Black Tree Monitors will actually be cheaper to keep in the longrun.