For the BCM vs. the S&W MOE, they are both mid length gas systems.
The BCM is going to have all of the "mil-spec" type features, if that is important to you. The BCG will be the full auto type, 158 Carpenter steel, HPT & MPI individually tested, and so on. Same with the barrel. Looks like it is a typical, standard type lower, M4 type stock, no sights, fairly standard rifle.
The S&W on the other hand, provides more features for the money, such as sights, all the Magpul furniture, Magpul marked lower with integrated trigger guard... lots of bling.
Neither rifle is truly "mil-spec", but to use the term the way marketing does, the internals of the BCM would be closer. I wouldn't say that makes one rifle more reliable than the other, but there have been more tests with a rifle built to "mil-spec", so there is more knowledge about how the parts will run together, wear, etc. You see a lot of BCM uppers on all manufacturers lowers, as BCM has middies and many others don't (looking at you Colt). Even though the S&W is not "mil-spec" it has many good features, such as the melonite treated barrel, and the S&W ARs have proven reliable as well.
The choice is yours, do you want your rifle close to military built standards, or do you want more features that change the way the rifle feels and handles? I would look around some though, as you can probably beat the Gander Mountain price.