Adding to the narrative in other answers, here is a chart that might help further explain why brass players tend to prefer sheet music written in keys with flats. As seen, written keys that exclude the “worst-to-play usual notes” (elaborated below) on common brass instruments (except French horn) are overwhelmingly keys with flats. This is especially true for almost all lower-brass parts, in which even the written-and-concert key of C, with no flats, includes the worst-to-play notes for all but C tuba and triggered trombone.
The specific keys mentioned in the question as being equally playable on B♭ trumpet— written keys E and A♭ — serve well to demonstrate this chart. The keys of E and A♭ contain 4 sharps and 4 flats, respectively, and are equally disfavored here because they include the trumpet's worst-to-play note, scored as C♯ or D♭.
Written keys WITHOUT
Worst-to-play worst-to-play
Name of Version of Open key usual note usual note
instrument instrument ------------ ---------------- ------------------
on score considered Con- Writ- Writ- Fingers/ How many How many
cert ten ten position sharps flats
F French horn 4-rotor F C G#/Ab 2-3 2,1 0 1,2
Bb Trumpet 3-valve Bb " C#/Db 1-2-3 1 0 1,2,3
Baritone T.C. " " " " " 1 0 1,2,3
Eb Mellophone " Eb " " " 1 0 1,2,3
Alto/Tenor horn " " " " " 1 0 1,2,3
Tuba C tuba C " " 1-2-3, 2-4 1 0 1,2,3
Tuba Eb tuba Eb Eb E/Fb " 6,7 2,3,4,5,6
Tuba Bb tuba Bb Bb B/Cb " 7 1,2,3,4,5
Baritone horn 4-valve " " " " 7 1,2,3,4,5
Euphonium " " " " " 7 1,2,3,4,5
Baritone horn 3-valve " " " 1-2-3 7 1,2,3,4,5
Euphonium " " " " " 7 1,2,3,4,5
Trombone slide only " " " 7th 7 1,2,3,4,5
Trombone F trigger " " C#/Db,F#/Gb 5th 0 1,2,3
“Worst-to-play usual note”
is an ad hoc designation
likely to find agreement among many players due to some of these factors:
•
The note is in the range usually scored for the instrument.
•
With 3 valves but no fingered slide,
timbre is compromised when a note is lipped into tune.
•
With 3 valves and a fingered tuning slide,
coordinating the slide quickly is difficult.
•
With an in-line 4th valve, pinkie-vs-ring-finger agility
is anatomically limited.
•
With a left-hand 4th valve, coordinating the hands quickly is difficult.
•
On a trombone, a quick slide excursion is a gymnastic feat.
•
French horn players have a right to complain as well.
Admittedly:
•
Almost-worst notes and convenient fingering/position sequences
play circumstantial roles as well.
•
Some rarer fingerings/positions are worse than those shown,
but tend to also avoid flat keys.
•
A trombone's 7th position is the worst of the worst.
An F attachment/trigger alleviates this.
•
As French horn is typically scored high in the range,
its usual worst fingering isn't very bad.
Have a different usual note that you least favor? Another instrument that would help to mention? Please comment or edit.
This comes from a community band and orchestra member who fills for whatever non-percussion parts are needed during rehearsals, playing the most appropriate brass instruments that happen to be along or available.