Well define best... LN2 will get the coldest readings, while phase change does a pretty good job with sub ambient temperatures. Of coarse a good liquid cooling system will outperform an air cooled setup. That does however come at a price both in the wallet and in maintenance.
Cheap water coolers usually aren't worth the money VS high end air. A 250 dollar Swiftech setup will smoke a 50 dollar air cooler, but is 200 dollars more.