If I:
- went inside for the evening as soon as it got dark
- was going to regularly have more than 2 adults spending the night
- need to store the camper in my garage
- am taller than 6'3"
...then I think would get the TM.
If I:
- planned on camping in the winter regularly where I would be in temps regularly below freezing
- like to cook outside
- want a larger refrigerator
- have a marginal tow vehicle
- don't need the luxury of a lounge chair or sofa (i.e. see above about being outside)
...then I think I would get a Casita.
Note also that Casita sells "Standard" (vs. Deluxe) models that do not have a bathroom. They are hard to find, but they have bunk beds or a sofa in its place, which would give you a fair amount more room.
As you said, they are both fine campers. I'd be thrilled to have either one.
Dave