ionesculxndr , usually Rockchip players are quite reliable provided you don't mess around with the firmware. Recovering Rockchip players have slightly better chance than Sunplus, but no less of a headache too.
You can read up more of the M6 here
http://www.meizume.com/showthread.php?t=12
The other alternative would be Teclast, as far as Meizu and Teclast are concerned, they are by far the most reliable. Also, both of these brands provide regular firmware updates.
In general, if you purchase them over the internet, be sure to purchase from a reliable source with reasonable warranty terms.