"Woodwinds and brass instruments are easier to play in flat keys. Strings are easier in sharp keys.

But all flat keys are also sharp keys, just with a different name. I mean B-flat is A sharp and so forth."

That's not the point, Kevin. Let me put it this way:   since a guitar is a stringed instrument, are you happier playing in G, D, A, and E than you are in F, Bb, Eb, or Ab? (And no, no capo allowed.)

It's because of the fingering. Fingerings in sharp keys on the guitar are easier than they are in flat keys. Among other things, once you get into flat keys on the guitar, you have fewer and fewer open strings available and you're lumbered with a lot of barre chords.

The same kind of fingering considerations apply to other stringed instruments. Easier to play in keys with sharps in the key signatures. A similar situation applies to brass and woodwind instruments. The fingerings are easier in keys with flats in the key signatures. It is a characteristic of the mechanics of the particular instruments in question.

The fact that if you wanted to play a Bb or an A# you would play the same fret or press the same key on a clarinet is totally irrelevant to what I am saying.

Don Firth