destroyer..first, welcome to the boards.
Now as far as the difference between ArmaLite and Eagle Arms, the major differences are that the ArmaLite line carries a Limited Lifetime warranty whereas Eagle Arms has only a Limited One year warranty. Eagle Arms line has chrome moly barrels where ArmaLite uses chrome lined and stainless steel barrels. ArmaLite also uses higher quality parts and forgings. This is why you see that the ArmaLite line is more expensive than Eagle Arms. Eagle Arms, however, is a quality made rifle that is priced to compete with other low priced brands. If cost is a mjor issue and if you don't necessarily need a chrome lined barrel and will settle with a chrome-moly barrel, go with the Eagle Arms.
Also note that you cannot buy just an ArmaLite lower receiver and receiver assemblies. You have to buy the whole rifle. You can buy just the Eagle Arms lower, if you wish, and attach an ArmaLite upper.
Whatever line you choose, you made a good choice with either ArmaLite and Eagle Arms.
ArmaLiter