Para Ord--excellent. I bought a used C-6 a number of years ago, had trouble with it, and posted on a 1911 site. I was contacted by George Wedge, Para employee who had been reading the forum. He asked me to send it in, which I did. They fixed it. Can you say "proactive"?
S&W--excellent. I bought a used revolver (M-396) and the previous owner had had used some sort of chemical that had removed a good chunk of the finish. I sent it in with a request for a price on a re-finish. S&W sent it back to me within a week or two, re-finished good as new...free of charge.
Ruger--excellent. My LCP was affected by the recall, although I had no issues. They paid shipping both ways, fixed it within about a week and threw in a spare mag and a hat.
Kahr--excellent. My PM9 (bought used) had the infamous barrel peening issue back around 2005-06. I contacted Kahr and they asked me to send it in. I asked if I could send the "top half" (slide, barrel, recoil spring assembly) so I would not need to use FedEx/UPS. They said sure, so I sent it in using USPS...$4.35 back then. A week later, I had a new slide, new barrel, new recoil spring assembly...and new Trijicon night sights (because they did not have a slide that would accept the XS Big Dot sight I had bought the pistol with. They would have taken care of that, but I was very un-impressed with the Big Dot, and readily took them up on their offer). Trijicon > XS Big Dot.
Springfield--excellent effort, okay execution. My EMP was an early production model (s/n 1705) and was a nightmare. Every form of malfunction a 1911 has ever had. I sent it back, they kept it for a month or more, and eventually sent me a new one (s/n 2750). It had almost every malfunction a 1911 has ever...well, you get the idea. I sent it back, they worked on it...IIRC I sent it back twice. Then I sold it to a local guy, with full disclosure at a big loss and with about five mags (got a free one every time sent it in...gotta give them credit for that). He sent it in once more. I'm sure the new ones are perfect. I hope.
Colt--not so good. Tried to buy a recoil spring assembly for a Defender several years back...no cooperation at all.
Kel-Tec...good effort, poor results. I owned four different K-T pistols (one P32, two P3ATs, one P11), which all failed to function as designed...a variety of problems. I bought new mags and a bunch of different ammo types, to no avail. I contacted K-T repeatedly, they sent me a variety of parts which had a variety of effects. Some problems were diminished, some were unaffected. None was ever reliable enough to carry, or to trust my life with. I sold each at a loss with full disclosure and will never...ever...own a Kel-Tec again.
I'm sure there are a few others, but these are the ones that I recall right now, so they are the ones that made a lasting impression.