We have most of the possibilities, a Kubota B series that is open station, a BX with heat only cab, a L series with a canopy and we recently bought a Case 480F LL with a full cab (heat only).
In the winter time, I love having a cab. Just something to keep the wind off makes it feel much warmer out (especially when snowblowing).
In the summertime, we take the doors and windows off of the cab on the BX so it becomes a canopy. We will see what becomes of the Case.
Cab, ROPS or canopy, you'll be much happier with life if you take a pole saw and cut back all the limbs that overhang where you're going to want to mow. You are far less likely to get smacked in the face with a branch that way.
The canopy does a nice job of keeping the worst of the sun off of you during the summer but your arms will still take a beating so wear sunscreen or long sleeves.
A cab without AC is going to be an oven in the summer, so I would recommend avoiding it if at all possible.
Down in Tennessee, I would lean towards a cab with AC if you need to get out and mow even if it's warm out.
Running AC is going to take a few more horsepower and give you another radiator that you will have to keep cleaned out, but I would think it would be worth it if you want to be able to get out and mow no matter how hot it is.
Aaron Z