I can recommend my Yamaha 613H - good sound, and easy-blowing.
I used to have an Edwards, which was a great trombone, but I had a lot of problems with the Thayer valves. The brochure doesn't tell you that yoiu have to take the trombone to bits in order to oil the valves, which took up a lot of time, and they clanked a great deal. I tried a Rath once and was most impressed, but experience with the Edwards put me off unconventional valves, hence the Yamaha. IMO, the valves on the Yamaha give just as good results as those claimed for Thayer valves, by the simple expedient of using "ordinary" rotary valves, but making them a lot bigger.
Conn have just brought a new bass trombone out, which should be worth looking at.