In your opinion, which gun has the best iron sights? Having good sights means you free up an attachment slot for any of your guns, so why put on an ACOG when the sights are good.
The best iron sights are on the ACR and the HBAR. AK-47 got some terrible sights
In CoD4, the G3 and M14 had good sights. I liked the M16 sights
The Tommy Gun and the FG42 in WaW were my favorite sights