iguana or monitor??

I think I'd advise a iguana over a monitor simply because a iguana can do far less damage to you.

I own a blackthroat, and did have a pair for several years. Moggie is "okay" but not trustworthy and I've had her a long long time. Wilson on the other hand I had fewer years, although he was an older lizard, and he was a raging jerk who attempted to maul me on frequent occasions. Neither was ever like a "puppydog tame" except for when Wilson was kept with no heat, fed a mouse hopper once a week in a bare cage. He was sure "tame" then. Once he was in proper conditions(I.E. not dying), he reverted to a more normal raging jerk behavior.

You kind of have to admire and love them for what they are, not what you think you can make them be(a scaly dog). Then if you do end up with a nice tame lizard, it's a great thing. But if you end up with a more normal jerkish monitor, it's nothing that you didn't expect going into it.

I think monitors eat far far more and it's more pricy diet than iguanas too. Both need huge caging and monitors need lots of dirt(which is heavy and a royal pain).

All that said, I do love my monitor Moggie. Also, have you considered an Argentine tegu?

It just needs to be added that proper Tegu care is up there with a Monitor as well

When researching any larger pet one of the first things you want to do is learn how it causes damage and to what extent. In the case of monitors and iguanas, neither dismemberment nor disembowelment are very likely, but you can get some serious damage from either - unless you choose one of the dwarf species and even some of those can do more damage than you might expect. I suggest you start out by googling "monitor bite" and "iguana bite" then read through some eye opening threads.