I use both. Flexwatt is really the best way to go because it costs much less to purchase, a factor to consider when buying for multiple enclosures. I have ultrathem pads on 2 herpcage.com cages and I have found by testing that ultratherm pads run as hot as the flexwatt when unregulated by a thermostat contrary to advertised information.If you were buying for only one enlosure and you wanted simplicity, ultratherm pads would be a fine option.