I need some help choosing which .308 system to go with. I would appreciate opinions from those who either own or have used one system or the other. Is either one better for multi-role than the other? How do they compare for accessory cost(mags, etc.)? If it's the AR10, which version is the best?

Any info is appreciated, thanks in advance!

AR10.
More accurate.
Easier to get parts.
Costs less.
Waranty.

FAL

AR10 the 91 is akward ecspecially if your left handed.

FAL,FAL! Plenty of parts on the market for FAL's. Mags are still reasonable, too.

HK91 is more durable and reliable, and mags and spare parts are cheaper.  AR10 has a better factory trigger and is easier and cheaper to accessorize, and is cheaper to buy.

Own a few of all three----look at FAL's!

neither of the above, go with the M1A.

AR 10 ! all ar15 parts interchange  pistol grip,slings, stock etc makes it more ver. and there is nothing like the buffer system  on the  ar type  they are the best weaopons in the world ,,,
  also  the armalite service  is simply  rated #1   did i mention the fact  that you can change calibers in about  10 seconds  .243to308  and back  also go from carbine to 20" barrel in same time    and the20 mag conversions  are only 30.00  from armalite and a rebuild  kit  finishes them off...50.00  bucks  not bad !  
LIFETIME WARRANTY !!!! LIFETIME WARRANTY !!    

H&K sheet metal receiver flexes too much (note reinforcing ribs on delux models) best magazines best internal parts (quality wise) it will eat and extract anything you feed it it will also eject your brass a half mile away ( you can get a deflector and brass catcher) lousey optics platform (claw mount sucks will seriously gouge up your sheet metal) but it is quick change and does work...AR10 better optical platform..gas system eh...it works..great service parts and expertise a call away cant beat that ..M14 mags weak link compared to H&K mags but are plentiful (for now)...FN great proven battle rifle plenty of parts cheap mags ...lousey optic platform...M14 reciprocating bolt handle great for gettin out of jams ...lots of parts and service ..proven battle rifle and gas system well tuned great accuracy....I carried both M16 and M14 in service all battle rifles are heavy dont get lighter with 20 mags extra ammo food grenades claymores
medical equipment or a radio....guess it boils down to what you are envisioning scenario wise....rural home defense Id take the AR10 or the M1A just my opinion and personal preferance and dont mean to slam anyones baby..FN never felt comfortable in my hand like the M1A does but I'm just a geriatric flatulator so what the hell do I know

Wasn't it an HK91 that jammed during the LA bank robbery forcing one of the two body armored assailants to switch to his pistol???

He was actually carring a H&K33 the select fire version of the H&K93 chambered in .223. I love my FAL, HK91, M1A, etc. I would take the 91 over the AR-10 just because I like the H&K system. ALL of my ARs are .223.