Does it make any difference whether  to use a "mil spec" buffer tube/stock over a commercial buffer tube/stock or is it just personal preference? Thanks for any info.

Steve E...........

If you are going to be using your rifle at the range, no difference. If you are going to be punishing it by going hunting (drops, etc.) or into combat, get the milspec. Milspec tube is stronger.

I have two Aero Precision lowers can I use either  (commercial or mil spec) with these receivers?

Steve E............

yes

Either will work. Just make sure the stock you get fits your choice of buffer tube as they are not interchangeable.

I knew each type buffer tube had to go with it's own type stock but wasn't sure if they would both fit the same lower. Now I know. Thanks for the info.

Steve E..........

One is not better or stronger than another. Actually a commercial tube is slightly bigger so it is stronger as far as the tube goes but a mil.spec tube does not have threads carved into the tube so it would be stronger at the threaded area. One is no better than another for actual use.
A mil. spec tube has threads protruding from the tube diameter whyle a commercial tube has the threads carved into the tube diameter.  Commercial tubes started because it was easier to thread a tube than it was to knock down the diameter of the tube leaving threads raised from the tubes diameter. The only real difference is when you slide on a stock. I actually have a commercial tube on one of my rifles that I sanded inside a mil.spec Emod stock to fit over. I like the set up because the Emod stock is perfectly snug rather than loose fitting like usual.