I like what Tom and Charlie (always good to see you post!) wrote. The 983, to me, is THE Eb sound. Not trying to be an average F, not trying to be a mini C,... I like a bit more tonal flexibility but otherwise it's just right. There are other reasons it's not my favorite (valve angle, comp low range I can't get with) but the sound is a-OK.
2141/22- Nice soundslikeaCbutohsobetter dark sound, good enough low range, but it really leans to the left when I play them.
big Willson Eb- Heavy but manageable; I'd LOVE to play a lighter version. A little tubby for me, but plays fine overall though a bit slow around low F/E. Marty is one of the coolest people in the world (ask him to play an scale without valves! or about playing hoops with Manute Bol!).

small Willson Eb- Friggin fun! Awesome, vintage physical feel to it, not my favorite sound (kinda small), but I could and have played it for hours. Still kinda heavy; a lightweight version would be golden.
classic 981 shaped horns- None of them play that noticeably different from the others for me. Big solid sound, agile for the size, awkward physically for me, for ME not the bestest low range, rather annoyed at the impossibility of being able to pull for low F and E and instead being forced to do lip stuff. There IS a youtube video of an English high schooler throwing continents in an orchestra on Prok R&J though! A front valve conversion to 4+1 or 4+2 (right and left) would be very interesting and hopefully shed a lot of the bulk. I have the same issue with Besson euphs, too heavy and tubby. Lighten them up and we got something!
front valve Kanstul- Nice big sound, rather similar to the 981 crowd, not the greatest low range (the Kanstul F is rock solid down there), can't speak to intonation. For what I'd use it for (concert band and quintet) I picked the Miraphone 1281; a little leaner overall but much better down low.
Miraphone Star and Light- Big one plays fine, not 100% me but whatever. Light is VERY lean, almost cimbassedly so. Cool but not for everyone. I don't find either of them to have the best low range, and even though Oystein wrote he'd be playing Prokofiev excerpts (presumably on the bigger one) with a trombone section I don't hear massive low register playing from him either. Mind bending cornet-like virtuosity, yes.

St. Pete- Solid horn, nice sound, good deal for the price. Feels very mildly flimsy here and there, not a huge issue.
My pick? A 983 converted to 5 or 6 valves (compensated thumb and 3 might be interesting but wouldn't give me the low range I want). None of the modern Eb's 100% do it for me. What I've actually decided to do? Check out small old Eb's, find the best one (got one that --might-- work with some work, got a lead on a cleaner specimen of my first Eb, a small Conn stencil with excellent intonation), and rock with it or get a new valve set. No modern horns give me the sound and playability I want in a bass tuba. Maybe an Eb version of the 622/821 Bobo F....

Or-or a Miraphone 1281. Excellent, excellent horn!