As we always say, it depends. It sounds like you don't already have a 7.62x51, so if caliber isn't a concern, the HK91 is the standard. More parts available, cheaper, easier to find. If you don't have any thoughts about getting another 7.62x51, get the HK93 for caliber consistency. If you intend on getting them both, I would get whatever you find the best deal on first. Also, the recoil management style is normally termed roller delayed blowback or just roller delayed. Good luck with your search!