The triple setup is probably going to work a little better as it has more area. It also depends on the thickness and even the types of fans on them. 280mm vs 360mm with just the fan sizes in mind. Also, the fin width matters as well. There's a TON of variables when it comes to radiators to look at.
Swiftech Dual 140mm "Quiet Power" Radiator... Quiet power, if not known, has a smaller fin density (12fpi).
Swiftech Triple 120mm "eXtreme Performance" Radiator... extreme Performance, if not known, has a higher fin density (20fpi).
Both are about 37mm thick.
If you get a higher density radiator, you have to get stronger fans (not CFM, air pressure) to compensate. But you will achieve better cooling than if you had a low density radiator with weaker fans (assuming everything else is equal).