well they both equally suck. If i were you i would stay as FAR away from motorolas as possible they are the WORST phones on the market. PLEASE do yourself a favor and buy any other brand.
There are various versions of both.If you are talking about the orginal in each line, the RAZR V3M and the RIZR Z6, some notable differences are:The RIZR has a 2.0MP cam vs. the RAZR's VGA cam. (.3MP)The RIZR plays music and supports STEREO bluetooth. (A2DP)The RIZR is a slider vs. the flip design of the RAZR.The RIZR supports expandable memory.A good tool for comparing cellphones is Phonescoop.com