I played both of those horns, but on different occasions. Both of the horns are excellent. I think you need to play them back to back.The prices are pretty close. If you go to Sam Ash, they will let you play both horns. Their prices are pretty competitive. I hope you stick with your playing, as these horns are very expensive. Practice On :)

ive played both and like said above u really need to play both of them back to back, but for a very generalization, now remember u can get any sound u want out of almost every horn, just one will lend itself to one kind easier, now that said, keilworth shadow will remind you of an old conn with a fat low end big bell, and just over all like a conn, then the sel,er really does do a good job of being like a mark VI(which ive played several) but the mark has a smaller bell so a tougher low end but can be just as fat with practice. Another thing to think about the selmer has a much tighter/closer ergonomics(key placement and feel) the keilworth is like a tank and big wide ergonomics. And to end this, there both great horns and i personally own a Ref 54, and never doubt my choice, i love it. P.S. im assuming ur talking tenor becase u said yts which stands for a yamaha tenor.