Aside from the latter using the name "Ripjaw", I don't see anything different.
More aboutwhats difference types memory
I didn't see any diiference in the specs. (or prices) either. But The Ripjaws have a higher percentage of happy customers.
G.Skill F3-10666CL8D-4GBRM is a later model, so i would go with it. Only $1 more lol.
IF you have an aftermarket Heatsink that is fairly large I'd go for the F3-10666CL8D-4GBHK -- the jaws of the ripjaw series do not really add to the cooling and can get in the way of the heatsink on some MOBOs