I have the 3x25, the 4x24 M2 w/ the BDC cam, and the 1,1-4x. I use them all on my 20" M16A4 SDMR in Iraq right now, and when I had an M4 before I became SDM I used the 3x25 on the 14.5". The scopes all came with reticle instructions,
I think the 4x24 M2 is the best bang-for-your buck in scopes. You can find them for about $330, and it's very fast to range with the reticle and dial in the BDC cam, which is pre-calibrated for M855. The thing is build like a tank also.
The 3x25 is a great ACOG substitute, especially once they start putting the new reticle in it, which has the BDC in the reticle.
The glass on these is Schott, and it is awesome.
Talk to Mike at CS GunWorks if you're looking for IOR stuff. I got mine from Green Mountain Tactical because they gave me a huge deployment discount.