^^^^^
What he said.

ArmaLite Inc

I have an AR10A2 from Armalite and it is sweet.

If you want to use the PMag magazines, you will have to get the "A" version; else, stick with the "B" version for their steel box magazines which are redesigned M14 mags.

Be aware that the Armalite design of the upper and lower will not allow other manufactures to interchange. Even barrel nut design may be different. But if you are just buying one ready to shoot and not planning to build one, that shouldn't be an issue.