yamaha maestro's are good instruments but remember that the top A's are a but tricky to place if your not 'in practice' - they are easy to split, in fact its easier to play a top C than an A on them. They are also a big blow compared to soverigns. I played oine for two years with no problem.
I have a Prestige which I bought after trialing other cornets such as Yamaha/Courtois/Sov's/Bach Strad to name but a few.
Prestige is a great instrument only let down by the valves, which i had sorted under guarantee, by a very knowledgable technician at Normans in Burton-On-Trent. Now the valves work brilliantly as well, and i really can't fault it.
Have also tried the Smith-Watkins and it is a very nice instrument indeed, it was the closest call to the prestige of all the other cornets i tried!!
So far as build quality, ease of blowing, response, and intonation is concerned, I don't think you can beat a Schilke, however the point has to be made again, as Mr. Lancaster pointed out [sorry, that's not terribly good grammar?], you have to consider the section blend; it's not easy to make a Schilke Bb blend into a traditional brass band section. And they're expensive. Still, if you're serious about getting the best instrument for you, then it's got to be worth at least trying one.
I have to say that if you can get an original 928 you won't go far wrong. Played on my old one, even though I had a newer GS, for about 8 or 9 years. The valves were reliable, not tempramental at all and had a nice sound in every range. I'm now playing the band instrument, a Prestige, it's better than I thought, valves aren't as relaible as the old 928, the resistance and blow factor is good. I did try a Smith Watkins when we invited them up to the band room, and I have to admit that it was very, very good, especially when they could be built to special individual traits/ It's a close choice for me, between the original 928, Prestige (whack the main slide out and play in an easier key!!) and the Smith Watkins (designed by Richard Smith who created the original 928 for besson (I think!)
At the end of the day I think its personal taste, reputation is one thing, personal comfort and state of mind is a far more reliable meter of which is best.