Some thoughts:
When I started with monitors, I wanted something that would be big. After dealing with male arguses, I soon found out that big was a major hassle. The bigger it is, the harder everything is for their care - just changing a water dish big enough for a big lizard is a chore. Also, past a certain size, the lizard will go where it wants to rather than where you want it to. And bigger lizards have the potential of being more destructive than little lizards - I've had arguses rip through hardware cloth and Niles dig through drywall. Of the three species you mentioned, arguses stay the smallest (especially if they are female) - so I would recommend an argus for that reason alone. Some of the smaller white-throats might also work. You could also look into flavies and Gould's monitors, which are sort of like smaller, calmer, sweeter tempered, and easier to manage versions of argus monitors. But generally, I would recommend getting some experience with a mid-sized monitor before jumping into caring for a giant like a salvator water monitor or one of the big races of blackthroat.
The one salvator water monitor I had was both very sweet tempered and very smart for a lizard. They are wonderful pets - but huge. I mean gigantic. You mentioned a 10 foot cage - this is likely to be inadequate. This is the sort of critter that would require a whole spare bedroom.
I have had many argus monitors, and they are certainly a lot of fun. They are active, pissy, in-your-face, full of attitude, always eager for food, tough as nails, but fortunately reluctant to bite in self defense (but don't get this fool you - they go into feeding frenzies when they think food is around and you definitely need to watch your fingers then). They don't back down, which lets you interact with them quite a bit. They get into more trouble than any other monitor I've kept, because they are always getting into everything and exploring. A ten foot cage should be suitable for a big male - the females stay a lot smaller and might get by with a six or eight foot cage.
I have never kept blackthroats. Those which my friends have had were typically good natured giants.
Good luck, and I hope this helps,
Luke