I'm sure others may debate this and please guys don't flame me, I'm just trying to help and this is by no means comprehensive or meant as an "umbrella" answer.
In my findings and I have all three makers...
Sansui 9090, AU-717 and a BA2000/CA2000
Marantz 2325/2265B
Pioneer SX-1250 and let go a SA8500II
The Sansui's are most sonically true, that is clean, transprent uncolored sound
The Marantz 2325 is known for it's 3 martini sound, warm, rich and romantic (too colored for my tastes)
but at the same time the 2265B doesn't seem to present itself like that at all to me. It reminds me more of the Sansui's. A little more clear and transparent.
The Pioneers to my ears seem to fall in between Sansui and Marantz. At times warm East coast sound while at other time more West coast, brighter and more clear. Actually the Pioneer sound is hard for me to describe.
There are so many variables to deal with here, speaker pairing, personal preference, types of music etc. that it's actually hard to compare their sounds. But in nutshell that's the way they sound to me.
For my money it's a toss up between Pioneer and Sansui. They're all powerful and have their own signature sound. Right now my Marantz's are spares and I rotate between the other two.
Now for the disclaimer, if I could have only 1.....my SX-1250. Floats like a butterfly, stings like a charging rhino!
I'm sure your question will be better answered later but I took a shot. Take your time,pick up pieces by them all and decide what YOU like. It's a whole lotta fun that way!......R1