mattz,
The only difference between the nylon & rubber Hogue grips for the SP101 is the material. Exact same shape, size, apperance and even cost (under $20 from Hogue to your mailbox). Both are completely interchangable. The screws are different between the wood and rubber/nylon grips though - requiring the stirrup to be changed as well.
The reason I got both was because the rubber soaks up a bit of .357 recoil. Rubber tends to be clingy on cover garments for concealed carry though. The nylon is not. Thus, rubber for practice - nylon for carry.
The wood grips are on my .22 LR SP101 that I use as a low cost shooting under study for the .357. I found the wood to be a bit too slick for concealed carry for me though (the nylon grip has the dimpling like the rubber - so not so slick feeling). But they are the same size and shape as the rubber/nylon. You can get wood grips with the checkering - but they cost more.