It is really not a question of "best", it is a question of what packs you are using. My only experience is with the e-Station PB-5 by Bantam. Will balance 2S to 5S packs, connect to any Li-Poly charger, self balancing capable, and includes the wiring harness for Polyquest, Hyperion, E-Tec packs. Optional wiring harnesses are available for Kokam and ThunderPower as well as an open ended harness for you to make your own.

If your packs are not one of the ones listed, you will need to get a balancer that has a wiring harness for your pack or give you the ability to make your own connections. The PB-5 is accurate to 10mV and can balance with up to a 5 amp charge rate.