Now that I have had more time with the new horn I wanted to give you the impressions you asked about. I'll post most of this on my forum as well.
Overall, it's an easy choice for me - the E3 is a better fit for my playing.
Physical feel:
The E3 feels larger to hold, in a funny way. I measured the reach across the main 3 valves and from the 3rd tube to the 4th valve button, and nothing there seems any harder to reach, so for most people this horn will be as easy to hold. But the body is a tiny bit wider, and the hand grip is positioned a little differently, which may account for it feeling bigger to hold. I'm feeling no extra strain when standing. The body seems to be rotated out just a bit more in this rendition of the Adams euphonium, so the right hand can be even more relaxed.
Tone:
In testing with many different styles of music, the E3 gives me more of what I want for 80% of what I play. The more intimate feel of the E1 is better in a few cases, but that is in keeping with the E1's somewhat smaller sound - it works well on "smaller" pieces that need a light sound. On the larger (i.e. louder) band and solo pieces, the E3 just sounds more "at home." My pianist noticed a difference right from the first day I brought the E3 to practice. The tone is just a bit deeper, even when playing parlor pieces.
Projection:
The E3 is the winner here, and projection was one of my main motivations for changing from the E1. When playing with an orchestra recently I had to work too hard to project with the E1. The E3 has more "headroom" when I really want to play loudly without changing my tone too much. In fact, now that I have been away from daily loud playing (in the Coast Guard Band) for 21 years, I learned that I need to change my practice habits to build up that strength again. I can overpower the E1, but so far I have not been able to overpower the E3 - it feels like I'm not quite getting everything it is capable of because my power-ability has gotten lazy!
Musical expression:
I did not expect this, but the E3 surprised me. Because of the extra headroom in the E3, I have the ability to be more expressive. Little bursts of volume happen more easily, for example. And yet I can also "swoop" down to very soft levels easily.
Ease of playing:
This one was a surprise. In my Besson days, I found the 968 easier to play than the 967. The 968 was a little smaller in feel, and it required less effort. But with the E1/3 I'm finding the E3 is actually the easier of the two horns to play. Interesting, and a little surprising. And getting down to individual notes, most are easier on the E3. In concert pitch:
- the upper G concert is a little harder to find so far compared to the E1, but I'm working on that.
- the tricky high B is a little more comfortable than on the E1 (and the E1 was already pretty good)
- the high D, Eb, E, and F are all better in tune and easier to play.
- the lower part of the 4th-valve range is not quite as free as on the E1 (which was well broken-in, of course). Low C (2 ledger lines below the bass clef) is harder to find than on the E1. That MIGHT be newness still. The same is true for B and C# in that same range. The pedal tones are also not quite as easy to play yet.
Intonation:
Overall the intonation is better, which makes the E3 even more remarkable in the current field of pro horns. I still feel that Adams has the best intonation of any euphonium on the market, and I'm still happy without a trigger. It would be nice to have the trigger for some of the 23 notes, but I'll happily "suffer" with that for the benefit of the lighter weight without a trigger. You can compare the two horns here if you want: http://www.dwerden.com/Intonation/
Judge for yourself:
Here is a string of 14 excerpts played on each horn. This was done in my church sanctuary, so the room is large enough to give each horn a fair chance.
https://www.youtube.com/watch?v=7Uc_Ag0bYiE
A recording does not fully capture the differences, but I think you can hear the tone difference in most of the excerpts. I had not had much time to practice the excerpts before running this, but I tried hard to play consistently. I actually recorded the first 8 pieces all on the E3, then all on the E1; then I did the next 6 all on the E3, then all on the E1. That was to help make sure I was playing each horn consistently. After recording, I broke each excerpt out and arranged them back-to-back as E3, then E1.
Most computers' built-in speakers may not tell you much. I'd suggest good headphones (not earbuds) or full-range speakers to hear the differences. It's fair say that the differences are a bit subtle on the recording (they would be more obvious if you had been sitting in one of the pews).