I too load for several different .308/7.62 weapons, including a M1A. As I do with all of my loads for .233/5.56 and 30.06 that may be fed to differing weapons, I fully process all brass (exception being those limited 'specialty loads') including descaling the interiors, multiple cleanings and full length sizing. So it comes down to the loading/s. I use 748 for most all .223/5.56 and .308/7.62 loads (see exception in above post). I have found a very suitable loading of 748 with 150 grain bullet that works very well and safely in my M1A and is 'wimpy' enough for use in my very light Remington 600. Note: I have deferred to H4895 for my '06 loads, as I feel they have better power/pressure curves for use in my M1 Garands.
So, to the point of this thread. I stand by my use of 748. I have not worked with all of the available powders that are out there and I feel that most are good. If not they wouldn't last long in the market. It is just personnel choice and tradeoffs for various attributes for each. 748 meters very well, is consistently available in my area, burns on the cool side, doesn't require 'Mag' primers, produces consistent load and I like it. And I can use it in several of calibers/cases that I load for.