I know it sounds simplistic, but any serious musician needs to work to play equally well in all keys. And oddly enough, each instrument has keys they like to play in. Guitars, Sax, Trumpets, Clarinets...sharp keys. Flutes, Oboes, Low Brass, Pianos...flats. Why? Because beginning bands and orchestras work in Concert F, Bb, C so nobody has too many accidentals. That means Ob, Fl, low brass are in flat keys, others in sharps. Guitars because open chords are easier to play and that make the CAGED keys easiest. Pianos - flats because starting with the key of Bb you keep your hands in the key bed instead of coming in and out for a single sharp here or there. You can almost tell who wrote the song (guitarist or pianist) by what key it's in. So, you, as an awesome musician, want to master all keys, so they are equal to you. So practice them all. At first do chromatic up. Jazz guys (which I am a) think the circle of 5ths is the bee's knees. But you get comfortable with whatever you do a lot so you've got to keep tricking your mind and fingers. The ultimate method is a 6 day rotation: chromatic up, P5 up, Whole Up (with a 1/2 slide after 5 whole steps), chromatic down, P4 up, and Whole down (with 1/2 slide at 5 whole steps). So when you're trying to master your instrument, work on all keys. (And vocalists, no telling what feedback will come with this, but there is no "good key" for you until you cross it with a specific song. The human voice can sing equally well in any key (or no key) until you stick it in a certain song, which then defines the high and low notes necessary. So "A is my key" really means "Lots of songs I like work in A for me", but the right sentence is "I like to sing Misty in A".)
It's amazing how much time can be lost in a rehearsal if people aren't serious. Makes you wonder what they're there for.