you usually combine the two, as air cooled peltiers SUCK. tec cooling is using a thermoelectric module to pull heat from your cpu (or wahtever) to such a point where its lowering the cpu (or whatever) to beign pretty dammned cold. however, they use A LOT of energy and add A LOT of heat to the system. a very good water cooled peltier is almost as good as phase change, but not quite. tecs main bonuses is their small size, and are often used to upgrade a watercooling system substantially after its all done (just add insulation, modify mounting, and wire it up to a power source). be careful, because a good size (230 watt tecs are popular) will DRAIN even a good power supply's ENTIRE 12v rail, so you need either a REALLY good psu, or an additional psu. hope it helps
