I reckon you might use most of the keys at some point but the chord shapes you know and use of capo will cover all of them anyway. I think I have a baritone range (either bass or baritone I never know) from a C or D two octaves under middle C up to an F (and on some things G) above middle C.

I sing Vincent Black Lightning in A
Summer Before the War in Bb
Tom Waits songs mostly in C
Whats the Use of Wings in D
Nearness of You in Eb
Rosemarys Sister in E
Will the Circle Be Unbroken anywhere between D and F#
My Love is in America in G#

etc

It's the range of the notes in the song rather than keys per se. You could probably sing most things that Ringo Starr did in ANY key as they had very small ranges usually!