As Pat said, that isn't an "either/or" question - a UTH is a heater and a thermostat is a device for regulating a heater. They're two different types of kit.
I run UTHs and control them with thermostats. In my experience, UTHs without thermostats run above the safe max for a Corn.
If you're going to use a UTH, buy a stat (if you're going to buy any heat source, I'd still advise using a stat or appropriate regulator).