In B and 2610 class, the prop of choice is the black MAS 9x4. In A class, the most common prop is the MAS 7x4. As mentioned, the MAS 8x3 is required for SSC.

The MAS props are used for a couple of reasons. They result in a higher RPM and while you get a lower straight line speed than an APC, the turning is better, at least in my testing with the 9x4. Most importantly, the MAS is about the most durable prop on the market, so it's most likely to hold together in a mid-air.