I think the problem with your thesis is that you are generalizing all of the categories. There are probably still some airlines with a crappy safety culture that you wouldn't want to work for. I know there are 135 ops that are nightmares incarnate. With Part 91 you have everything in the spectrum.
You asked for experiences, so here's mine:
Part 91 for Fortune 150ish publicly traded company. The "publicly traded" is important for your QOL. It means any non-business use of the aircraft gets charged to the user as imputed income. That translates to almost no weekend flying at our company.
We have an ops manual that incorporates a SMS. The manual was signed by the CEO as company policy. We do not violate the manual for any reason. Our passengers know this, and know that we have the CEO's ear. Of course we get asked to do borderline things (duty times, etc...) frequently. In the 12 + years I've been here I've never been second guessed when I've said no with a professional explanation.
We are paid average, (or maybe low average?) for the aircraft we operate (large cabin Falcons.) Benefits commensurate with a large manufacturing corporation, 5 weeks paid vacation after a couple of years, stock, 401k match, discount programs, etc...
We staff at 3 pilots per aircraft. Every pilot flies around 350 hours a year, or 8-10 days a month average. We are not expected to show up at the hangar on non-flying days. While we are a pretty diverse group, our culture is one of professionalism. I can't imagine anyone skipping a checklist or operating against SOP.
So my experience is that there are really good Part 91 operators out there. Also really bad ones. In my opinion one of the best ways to tell the difference is pilot turnover. My company has had a flight department since 1984. We have had 7 pilots leave in all that time. Only 2 left to other flying jobs (United and Southwest.) the other 5 were retirements or career changes, one of which to upper management of our company. We've had one pilot opening in the last 10 years, to replace the United pilot last summer.
Personally, I started flying in 1984 too. I've watched the industry boom and bust. If I were in my 20s or 30s now, I'd go to 121. The career earnings of even the best 91 gig aren't going to compare to 30+ years of mainline 121 pay. However, the trade off is endless hub flying, TSA, and dealing with passengers, in the terminal and in the air.