I would say in general, tegus are far more docile and easier to tame than monitors are. However, there are exceptions in each category. Gold tegus are notorious for being more aggressive as are nile monitors.
Have you ever owned a reptile before. As a word of caution, it is a HUGE committment. Be warned that monitors and tegus grow extremely large and will require atleast a 6 foot long cage when full grown, possibly larger depending on the species/sex. Also, you should know that financially, buying the actual specimen is the cheapest part of caring for a reptile. Building/buying a 6 foot long cage will cost hundreds of dollars, and daily feeding will be quite costly as well. And you'll have to be prepared to change the substrate quite frequently as these are large lizards and take large poops.
Having said all this, if you feel that you are willing to accept this challenge for 15+ years, then by all means get a tegu. I myself have a female blue. She has never bitten, or even shown any form of aggression toward me. Female blues are also the smallest of the tegus (with the exception of "dwarf tegus"
. So it is basically at matter of choice, you can't go wrong with any species of tegu, so long as it isnt a gold, just keep in mind that females will be smaller.

Amika photos and video