I like them both, and I can already play the guitar pretty well, but I love jazz music, and all my favorite players are horn and sax players (besides drums and bass of course). I just don’t know if the electric guitar fits into modern jazz very well, free jazz and stuff like that.
Guitar.
It allows you to play chords and melody, and the fact that you already know how to play it makes it a lot easier. The great thing about playing chords is you can play while other people are soloing, adding another level of interaction.
There are lots of electric guitars in modern jazz, if you get out of the horn dominated stuff. Look into guitar groups and artists like Jim Hall. And tonally guitar and sax are often utilized in a similar manner from an arranger’s standpoint. I can’t count the times a big band director has given me a sax part to play.
as to free jazz – I’ve had a few killer free jazz jams that were nothing but two guitars and a mandolin. And a few more that were 2 guitars, a bass and a high hat/snare ‘drum kit’. It’s the mindset of the music, not what instruments play it that matters.