Any of the three are solid rifle designs.
Ergonomics... the Fal is better for most people, but you really have to get your hands on each to find out what's comfortable for you. The Cetme and HK design has a rather long reach for the safety selector, for sure.
Personally, I find the FAL an ugly beast. Just don't like the look.
Don't know much about the Cetme, other than it's history as the predecessor to the H&K... Most that I've seen look pretty primitive.
I bought my PRT91 because I liked it. It was sitting on a shelf next to an AR10 and a DSA FAL... all within a few hundred of each other. I picked the PTR on looks, and how if felt to me. Didn't really know that much about the action at the time, though I had heard it was known to be quite reliable.
PTR mags are cheap and plentiful, but so are FAL's really...
Downside of the PTR is that you can't really reload for it. Mine throws it's cases quite some distance, they all have a fairly severe dent in the neck area, and soft brass shows the impression of the chamber flutes all along the sides. Not exactly gentle on the brass. I started shooting steel cased ammo, and couldn't be happier with it's performance. It's cheap (as .308win goes, anyway), reliable, accurate enough for my purposes, and I don't have to worry about scrounging for brass.
Hard to go wrong with any of these choices, as long as you get a good quality example of the Cetme or Fal (the PTR's are quite good... some would say better than the originals!)