My favorite overall are Leafcutters and seed specialists (like Veromessor and Pogonomyrmex)
However, my favorite ants to keep are probably Pheidole megacephala, despite being an invasive species. I don't have any now and I don't live in the area anymore, that they are in. But, super clean species, super easy to keep, incredibly hardy and they are semi-subterranean so they don't tend to want to escape much. Compared to Solenopsis invicta, Ph. megacephala are vastly easier and S. invicta is already really easy. They also readily breed in captivity (unlike S. invicta) so they are an immortal growing species that has no end.
Can't think of an easier species than Pheidole megacephala, don't think it gets easier than them.