I've owned both AR15's and AR10's (.308). There are many different calibers available in these platforms. If you are looking for something to plink with and target shoot, go for the .223 (5.56). If you are looking for something more powerful, butstlll lightweight, try the 6.8 SPC, or 6.5 Grendel. If you want something really badass, go for the AR10 (.308). It is a little heavier, but much more powerful. Overall the platform itself is one of the best in my opinion (as far as assault/tactical rifles go). You will not be disappointed.