Sansui or Marantz.
Nothing wrong with Pioneer, Yamaha, Kenwood, Marantz, or Scott, but I'd rather have a Sansui.
Are you going to get a 30+ year old amp? Chances are you will have to restore it. Work that into the budget.
All these amps/receivers are older which is a 'primary concern' for true sound and stability, it's just a fact of life. Restoration is a primary concern. And who's going to do it??? And where is he/she located? Will you have to ship it? These old amps are heavy, it's $40-$50 one way if your going to ship it.
Which one to get? Whichever one 'functions stabily, operates the best, and sounds the best to you. Has the amp you are going to buy 'stock' or has it been messed with by unqualified techs?
Sansui's got the 'sound, the transformers, and the power'. I prefer Sansui.
It all depends on how you are going to use it and exactly what your musical tastes are. Do you need Watts RMS or is it for easy listening, not a lot of watts required. What speakers are you going to be using? What type of TT and Cart are you using? If you got a great tt/cart, you want a great vintage amp with a deep sound. 70 Watts RMS is a good working number. It's got power. You can crank it, if your into that.
What will you be listening to primarily?
Yamaha(s): Nothing wrong with the old Yamaha(s). They sounded great and were BIG sellers back in the day (era early '70s). Yamahas Rocked!! And sounded great!! Everyone loved Yamahas. Maybe they didn't buy one...but they liked them a lot!! But honestly I really don't know 'how Yamaha(s) aged'. Haven't heard a Yamaha in since 1972.
Do you want an amp or a receiver? Sansui's 9090 and Gs are muscle machines. The AU-717 has a sound that is unreal, a really real 'deep' sound, a true workhorse, like a live-on-stage sound - same with the AU-919, and both sound outstanding with records. The TU-717 is an audiophile grade tuner. Great combo. But...they have the dreaded glue problems on the boards, which many older amps have, so during a restoration the glue will have to be removed and componets eated away replaced.
All the older 70's and early '80s amps will need a total restoration sooner than later. Which is expected. If you have a good vintage tech in your neighborhood, that's vital.
Which ever one sounds the best to you.
I really do miss my old AU-717. Still have the TU-717. I'm presently using a '87 Sansui AU-X901 'Vintage' (130W) and love it. It's an audiophile sound but still have the sound of the older circuits. But it's younger brother, the AU-X701 'Vintage' (100W) is a really nice amp too and sells for about $250 used, which is a real good deal. Saw one sell for $94 once! That guy got a super deal!. It's a great amp for a very lower price if your on a budget, and it's '87, so it's newer. The X901 sells for $500+. Both are top quality throughout.
If your on a real limited budget...even the '87-'89 Sony receviers sounded pretty darn good really. Suprisingly so.
Don't be in a hurry to buy, take your time, do your 'research!!!", and get the right one.
Hope this helps.
Good luck!