Hi, first, I think most all of use who have bred varanids, did it for the same reasons your asking about. behavior, fun etc. Money from offspring is simply a product of good husbandry.

Monitors are not like many reptiles. You do not need to hibernate, photoperiod, rain cycle, etc to get reproduction. You just need a healthy socialized pair. And lots of food.

Its also a very hard question as each species has their strong points.

So I will with the gould group, Flavirufus, gouldi, and panoptes.

With Panoptes being a bit of an aquired taste. hahahahahaha as in, they can be super active and super interesting, to a point you super can not take it. hahahahahahahahahaha

Flavis come in great colors, as do some of the crosses.

Yup that group is just plain fun. Cheers