I would only use a rheostat if the temps in your house stay relatively constant. Back when I was in HS and lived at home, my parent's house stayed right around 70 all year long, so all I had were rheostats. Once I moved out, my new place fluxates between 70's at night and up to 80 during the summer, so I've switched to thermostats. The rheostats in that situation just fluxuated the temps way too much.

So yes, if you have steady constant temps, rheostat is fine. If not, go thermostat.