I voted other, as I use both. The main difference between the flexwatt and the UltraTherm is that you CAN get away with not using a thermostat with the UltraTherms (though definitely NOT recommended). With Flexwatt, you have to use a thermostat, no questions asked.

I have Flexwatt on all of my tubs and I use the UltraTherm heat pads when I do outreaches with snakes as they are easily portable.