Several months later...
For Underrated:
Yamaha - I have no clue why people don't like Yamaha that much, I always liked their stuff. Nice build quality and very clean. I wish I could find more of it, but it's quite rare in any form.
Technics - Maybe I'm biased because my first receiver was a Technics, but I've always liked Technics equipment. Most of my experience is with the late 80's and the 90's gear and I like most of what I see. I have never had a Technics anything that didn't work perfectly. Only once did I find a vintage Technics that had a fried power supply, but it was an entry model Technics. I love my Technics CD player and wouldn't replace it for nary anything else.
Onkyo - I don't ever hear much about this stuff, but I have always liked Onkyo stuff. Onkyo didn't really cheap out in the 90's, still had nice metal on them and had some heft about them. The vintage Onkyo I see is also pretty nice, but very uncommon - I have yet to see a vintage Onkyo anything in person.
Now to the overrated stuff...boy some people aren't gonna like me for these but whatever, I'm not saying it's BAD stuff, just way overrated...
Marantz - boy, I'm tired of hearing people go on and on about Marantz stuff like it's so wonderful. It's the same level of quality as the other old vintage gear that is well made I've found is. Except it's not too reliable, we had a Marantz before and it had a problem with the speaker terminals and a few of the RCA phono connectors didn't work right. People ask high prices for this stuff and I just don't see it. That and when you see them describing it, they are just gushing about how wonderful it is and how they're so firm on their ridiculous price...and for about half the money I can buy a massive receiver or something from any of the other companies of the period. I also don't like that spin wheel for the tuner - I like my dials!
Pioneer - Almost every Pioneer I have personally owned has had stuff wrong with it. I had a vintage Pioneer SX I think a 9930 or 939, and it had lots of quirky issues with the speaker selector not wanting to stay in, tuner was come and go, had some other annoying problems. I have a much newer fairly mid-fi Pioneer surround receiver, the volume on it doesn't work on the front - rather it only goes UP and not down so you must use the remote. Not to stray too far, but I had a new Pioneer blu-ray too and that thing was pure rubbish. To be fair though, I have my Pioneer PL-71 turntable and it is quite nice - works great and I do love it. But I'm not a real big fan of Pioneer...
Sansui - See above...seriously, every (Yes, I do mean literally every) Sansui I have found has not worked properly either. Be it entry level or flagship model, they're always broken! I had a 9090 not too long ago - and that thing I just could not make work and saw nothing that should have been wrong with it. I hate quirky problems...they frustrate me to no end. Although Sansui stuff generally tends to just flat out not work in a useful way (i.e. - no output to the speakers, amp won't come out of protection, etc.)
Of course I'd still buy any of those I mentioned, it's just that I'm not particularly a fan of them. I seem to have a thing for the less mainstream brands. I like me a nice clean NAD or Adcom! I like low frills, but high quality - hence I usually don't care for vintage receivers with all the lights and stuff, way too showy (Many still sound good though).