Having owned all three (the Galil was a .308, though), I clearly favor the M1A hands down. But there are a couple things to clear up first. Do you want .308 or .223? You said the Galil was the latter, so it isn't really in the same category as the other two. If it were me, well I prefer .308. I like the reach, power, and penetration of the round. If you are not sure, research that further. Of course if you can buy another rifle later, it may not matter much as you can just buy the other caliber then.
Second, how much can you afford to spend? Since you said you were looking at a Galil, I will assume you have plenty of cash as they are pricey. If you are looking at a post-ban clone that may not be the case. If you are needing to stay cheap, I am not sure the FAL saves you much but it can save a few hundred over the M1A due to cheap mags. I would not buy a cheap FAL. I have had a couple, and found them junk.
If cash is not an issue, then cheap mags are not an issue. I would hate to pick ones gun based purely on the cost of one component of the whole weapon system. I simply include the mag price in the total cost of a gun when I buy it, factoring in X number of mags where X is what makes me happy. So lets look at M1A mag costs. While mags for it are in the $40 range sold individually, Coles sells them by the 10 for as little as $30 each. 10 is probably plenty, and if it is too many for you then sell a few for $35 each.
My reasons for picking the M1A over the FAL were subjective. I have fired quite a few FALs and never found one that touched my M1A standard model for accuracy. The most accurate FAL I fired would print 2-3 inches at 100. The cheap ones were more like shooting an AK--in fact less accurate than my Vepr K or Saiga in 7.62x39. The M1A is reliable almost on par with an AK when using USGI mags. I have yet to have a malfunction. The FALs I had were pickey about ammo, and the gas system had to be adjusted to get them to run right. The M1A recoils less by far. I know people say the FAL does not recoil that much, but I have fired many and never found one that recoils as little as an M1A. The M1A fits me well in its shape. YMMV. I shoot left handed, and like the fact that the safety is ambidextrous. I also like the right hand charging handle so I can manipulate it while keeping my trigger finger ready. Mags are easily inserted by either hand.
The M1A also lends itself to customization, although thanks to DSA and Tapco there are a lot of options to mod the FAL now. I have cammo fiberglass stocks on two of my M1As. This makes for a nice look, and lightens the guns a bit. I don't mind their weight anyway. You do get a very effective flash suppressor on the M1A. On the FAL you can only get that on a preban legally. The flash is next to nil on my Standard if that matters to you. Some of the FALs with brakes have much worse flash than no brake, and a lot of blast. If the brake does anything, it may be worth that to you. Some brakes don't do much but enhance the blast.
Now having said all this, I must tell you the best thing to do is handle and shoot examples of both the FAL and M1A. Some guns just fit some people better than others. I still own one FAL for that reason, that I plan to pass on to my son when he is old enough. Who knows, he may like it. But then, he also gets my M1As--when I am too old to shoot them!
GR
