I own a HK91 clone; my roommate owns an FN-FAL. I like mine and he likes his :)
Both are about as accurate as each other - we can each reach out and touch a man-sized target at 600 yards with the iron sights. His FAL has jammed, but we found out that that was mainly due to a durability test he was running on it (he hadn't cleaned the poor thing for probably close to 1000 rounds!). We were able to dial up the gas port and have it blow through the crud, but... The HK91 jams occasionally, but that's when I haven't cleaned the mags in a long time (I use thermolds). Open the mag, clean it out, and it's good to go again. The FAL has broken a few parts; nothing has broken on the HK91 yet.
The HK91 is more expensive, and so are accessories. The bolt hold-back on the FN-FAL is a nice touch. The HK91 has a really heavy trigger, but gunsmiths can fix that. Even if you don't.. well, if you get used to that trigger pull, you'll think that everything else is wonderful! :)
The HK91 is a taste easier to clean, but it's harder to get into the receiver to clean all the nooks and crannies. The FAL breaks apart into a lot of little pieces; on the HK91, all te little pins get put into holes in the buttstock.
Overall, I'd say they're about equal. Maybe the features tip out a bit more towards the FAL, but I like my HK91 clone, it's reliability, and it's accuracy.