I went with the RIBZ since it also gives you the IBZ and BZ as well. That way you have the 25, 50 and 100 meter zeroes if you want. You just reindex the elevation wheel about six clicks instead of the IBZ's four (if you have the removable carry handle). The info threads talk a lot about A1 and A2 so remember to use twice the clicks if you have A3/A4.
It's a lot of fun but I don't mess with it anymore since I went with an RDS and rarely shoot over 50 meters. I'm back to the good ol' 25 meter BZ.
One thing to keep in mind, what distances will you normally shoot... The 50 meter IBZ is great if you want +/- 2.5" from 0 to 220 meters.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek