I'll concur with those who point out that it is the player and not the horn; and with those who pointed out this thread is just another popularity contest. I'll add that with a few exceptions, most of the models I've owned/played vary in tonal effects merely because every horn is usually different from other similar models.
With modern altos, I've owned several different models mentioned above including Yamaha, Yanagisawa, Selmer Ref 54, R&C, JK, and Unison. With vintage altos, I've owned Buescher, Conn, King, and Selmer. In thinking back through all of them, only a few stick in my memory - and not because of the way they sounded (they ALL sounded like altos), but for the way they sang to me, the way they responded, and for their intonation.
AND, I'll offer that no one should reach a conclusion about tone based on only one or two examples of each brand and era. However, in my travels and retail searches, I found ONE model that had a different tone from the others and which was consistent across the six or more versions I play-tested before buying one. And that was the Reference 54 alto.
I now have in my closet a '25 King, a '32 Cigar Cutter, an early '60's MKVI, a Ref 54, a Buescher Big B, a Buescher TH&C, and a new Yanagisawa A-WO1. Of those models, the A-WO1 is my favorite, followed by the Big B and the Cigar Cutter. But not just for tone, but for overall ease of play, response, and intonations.
The ONLY way you are going to answer your question is to play them all. And the end-result may be that the one you choose may have been the one with the best set-up rather than design or brand-name. DAVE