[Bognar]

I highly recommend any cube from Dayan, but this is my favorite:

http://www.amazon.com/dp/B008U6V50U

It's smooth as butter, and there are no stickers to cheat with.

[captn3m0]

Stickerless cubes were until very recently illegal in competitions. The new regulations (in effect from July 2015) allow these now, meaning a stickerless Zhanchi is a really good purchase.