I don't have an M14/M1A, but I do have one M1 Garand with another on the way from CMP, and a CETME that's one of the good ones (pretty close to a HK91). I also have an assembled-by-me FAL that's an STG58 on an Imbel gear-logo receiver plus a bunch of top-notch 922 compliance parts. Both of my rifles are equally reliable, and are just about the same accuracy-wise - with my eyes I shoot 3" groups at 100 yards.
My take is this:
The HK-system rifle is pretty rude and crude, with a really bad trigger. Also the ergonomics are really bad. Firing it, you hear this big "schwaannnggggg" noise next to your right ear as the bolt carrier cycles on the buffer. No bolt hold back. The rifle also doesn't seem to balance very well, like it's top heavy. Mags are cheap, though - it's only good point - but all in all I would prefer either the M14/M1A or the FAL over the HK-system weapon.
Now, to evaluate the other two choices (and remember, my M14/M1A comments are based on the Garand, which, except for the en-bloc clips versus a removable box magazine, is pretty much the same rifle):
M14 mags are sooo expensive, compared to the FAL metric mags. Advantage FAL.
M14 gas system is a little fussy with that long funny-shaped operating rod compared to the FAL's straight piston. Advantage FAL.
M14 has a stronger gas system in terms of extraction and cycling, since it's a long-stroke system as opposed to the FAL's short-stroke system. Advantage M14.
M14's gas system is non-adjustable, unlike the FAL's, but with the strong long-stroke operation maybe this isn't such an advantage. I'll call this one a draw.
M14 has a stock that permits use of the sling as a shooting aid, compared to the FAL's barrel-hung front sling swivel. Advantage M14.
M14 is MUCH harder to field-strip than the FAL. Advantage FAL.
M14's sights are several orders of magnitude better than the FAL's. Advantage M14.
M14's sights won't come back and smack you in the eye under recoil like those of the FAL. Advantage M14.
M14 probably has a better trigger right out of the box, but my FAL has DSA H-T-S parts and has a pretty darned good trigger pull as well. I'll call this one a draw, too.
So, here's the score:
M14 - 4
FAL - 3
Draw - 2
Pretty close, and a lot of the criteria that I use for evaluation are pretty subjective. Bottom line is, I don't think you'd be under-gunned with either one.
Somebody suggested a Garand from CMP. Actually, that's a pretty good suggestion. The one I have is 100% reliable, and shoots into a 3" group at 100 yards with my 55 year old eyes behind the sights.
The en-bloc clips are not as big a disadvantage as everyone thinks they are. Remember, with a box-magazine rifle, when you shoot it dry, you have to reach up and find the mag release, remove the old mag, get the new mag, align it correctly, insert it and lock it home, then release the bolt.
With the Garand, when it goes dry, it ejects the empty clip out the top and locks the bolt back for you. All you have to do is grab the new loaded clip, orient it with the bullets forward and one of the skinny sides down (remember, there's no top or bottom), and shove it in until it locks. Sometimes you have to nudge the bolt, sometimes it goes home on it's own. It can really be reloaded pretty fast.
I once read of a comparison test between a Garand and an M14 where they timed two guys firing and reloading as fast as they could for something like 3 minutes (don't remember, exactly). By the end of the time period, the Garand had actually fired more rounds because it was quicker to reload, even though it had to be reloaded more often.
I would also stay away from the "scout" version of any of the rifles, as all the shorter barrel gives you is a shorter sight radius for less accuracy, more muzzle blast, a loss in muzzle velocity, and possibly reliability issues - maybe having to enlarge the gas port, etc.
But the HK91 would be my last choice.
