They would both do the same thing but you'd want the one that covers more of your body. But I think these little portable ones won't give you anywhere near as good results as a regular sauna enclosure with several infrared emitters. You can get a whole infrared sauna now quite cheap, like the Saunagen, which is about 3 X 3 X 6'. I've seen them on the web for as low as $1500 US.
I"m building a one person sauna. If you know someone with basic capentry and wiring skils, build your own! I bought 8 infrared emitters from promolife.com for $35 US each and I'm building a 4 X 4 X 6' sauna. I found some cheap tongue and groove cedar for the walls (you could even use cheap $1.50 1X6 fence boards at Home Depot) and with the wiring and emitter housings I'll make out of aluminum flashing, the whole project will cost me less than $500 CA
Another alternative is the very inexpensive infrared light option. See www.drlwilson.com