I run a number of different batteries - from stock eflight, sky lipo, gens ace, to haiyin.
For my money and usability, I like the Haiyins the best. The combination of performance (at least equal to my gens ace), wire length/positioning, and price, these can't be beat. Additionally, they have a support presence on rcgroups and respond on the forum regularly.
I plan to buy a couple of their 6s batts soon.
http://www.haiyinstore.com