Hi,
From personal experience, I can recommend
MP4 Nation.
It's actually run by one the regulars here - razzer001.
They deal only in decent players, and you will certainly get a genuine item from them. I'd recommend Rockchip units as well (generally called Optimus units on mp4nation), or if you want to spend a bit more, they have some great players from Ainol, Hacha, Meizu etc.
Good luck!