My personal favorites are drums and bass guitar/double bass, but I suppose that's my player's bias. I have the most experience on bass guitar and have played primarily in jazz/blues ensembles going on 3 years now. I have a want (and need) to get better at guitar, but I consider it a bit more of a "specialist" instrument for the kind of stuff I fancy. Truthfully I only want to improve as a blues/jazz soloist on guitar a la Eric Clapton's early work or Henry Vestine/John Lee Hooker.
I've only played a few gigs where we didn't have a Hammond B-3 on hand. They're fantastic little keyboards wit