Most species really should just be displays, some of the tarantulas out there will rival a dart frog display, and nothing beats seeing these little slings turn into big monsters after 5 years of care, the market for some of these species is huge, you can buy an avicularia versicolor sling for $8 yet a 5"female easily fetches $450.......hands down some of the easiest care requirments as well.
Ive been sitting on about 300 slings for 3 years now raising them for pairings, it can be extremely slow for some species that grow 1/2" a year...