Have a set of 10" and 9" rims Both are .190 wall which on to use for desert playt riding??

 

9" will give you more sidewall and more cush, for a more comfortable and forgiving ride. Might feel a little mushy in hard turns, as the sidewall gives.

10" builds a lighter wheel, because rim is lighter than tire (less sidewall). Ride will be a little more harsh, seeing you don't get the cush of the taller sidewall.

But frankly....most folks could never tell the difference between the two!

My choice is ITP Baja 9X9" rims with reinforcement rings, with Holeshot XC tires (or XCT's when I need max ground clearance). Best combination I have found after searching and trying many different rims and tires for years.