Most of the LED controllers that you can buy are eight bits. However, there are controllers that provide more data bits for the brightness, such as the TLS3001 or CYT3001, which have 12 bits. In fact there are controllers with 16-bits of brightness control. Which type you buy depends upon many factors, but lets look at the supporting hardware and software.
First of all, looking at the software; Vixen, Vixen plus, HLS, and Nutcracker, they all support only 8-bit data per channel for lighting. If you look at the transport protocols; DMX, Renard, ACN1.31, and pixelnet, they only support 8 bits of data per channel. And finally, most of the controllers also only support eight bits of color per channel. The software support for sequencing is probably the most important.
The SanDevices controller has mapping to convert the 8-bit data to 12-bit data. This is a good thing since you can map the brightness to the perceived brightness. Basically, you get better dimming at the lower brightness levels. For eight bit pixels if you do a slow dim you will see the steps in brightness at the dimmer end of the scale.
One more thing to consider is the accuracy of the pixels you have bought from China. These are low cost, low end parts. So you get what you paid for, the white color will not match from LED to LED, and many of the controllers do not specify their brightness accuracy. The data sheet for the TLS3001 indicates that the worst case accuracy between chips is ±6 percent, which is only about 4 bits of color accuracy.
So if your expectations is to display simple cartoons or colors on your LED’s then eight bits will be sufficient. If you want color accurate LED’s for video, then you need color matched LED’s, more accurate power supplies and controllers. For me the color matching to the computer colors is more important, which can be provided through gamma correction.