I have one of the first PTR-91's (serial number 10xx), with the early polygonal rifling. I understand that some time after mine was made, JLD Enterprises switched to using cut-rifled barrels. I don't know whether that made a difference in accuracy, but mine is a tack driver.
Also, as someone mentioned above, JLD Enterprises was sold in the last year, and the company was renamed PTR-91k, Inc. I have no idea what the sale of the company will mean in terms of product quality, but I've heard nothing to indicate it would be a cause for concern.
In general, the PTR-91 is an excellent rifle. It is built using HK-licensed tooling that was originally used in Portugal to make G3 rifles for the Portuguese military. The triggers are indeed terrible, as are original G3 triggers. When I got mine, it was heavy and creepy -- like dragging a sleg over a gravel bar. It was so heavy, in fact, that it maxed out my trigger pull gauge (12 pounds) without releasing. The good news is that they can be improved. Bill Springfield did my trigger, and it now breaks cleanly at 5 pounds with no creep. He also took out the slack and overtravel, all for around $50 including return shipping (you just send the FCG -- no need to ship the entire firearm). One of my buddies is a benchrest shooter, and he was quite impressed with the trigger.
I didn't have any sight issues with mine. It was easy to zero with an HK sight adjustment tool. I did scope mine with a TAPCO reproduction of the HK "claw" type mount and a STANAG-to-picatinny adapter. It works well, and keeps the irons visible under the optics, but it puts the scope pretty high above the bore. I added a snap-op cheekpiece to the stock to allow a good cheekweld with the scope.
The mag release is also a pain, but of course that's because of BATFE-mandated changes to the G3 design (intended to prevent installation of G3 selective fire FCGs). If you're not going into combat with the rifle, it doesn't matter. If it bothers you, there are two options. One is to have a G3 paddle installed. That's a job for a pro gunsmith, as it involves some cutting and welding, and refinishing the receiver when you're done. When I looked into it a few years ago, several guys did it and the going rate was around $200 with parts. Instead, I opted for a "Tac-Latch." The Tac-Latch is a drop-in paddle mag conversion that requires no mods to your receiver and no refinishing. Unlike a G3 paddle, however, the Tac-Latch paddle moves side-to-side instead of front-and-back. If you ask Tac-Latch, they'll say it won't fit in a PTR-91. I made it fit, however, just by using the bench grinder to radius one of the Tac-Latch components a little. Total install time, including mods to the Tac-Latch parts, was less than 30 minutes.
Here's a pic of my PTR-91. The wide forearm with bipod is a surplus G3 part. You can see the Tac-Latch paddle just behind the mag and forward of the trigger guard:
