If I was able to include having a band, then bass all the way.
If it's just me & no band, then keys. Preferably a moog voyager, korg kronos or nord stage, but I doubt I'd have the funds. So maybe a korg m3 (yes, I'd been considering it when I was bandless & might still if the band's a no goer).
I play guitar, I wouldn't choose it over the majority of other instruments as everyone who wants to play an instrument plays guitar & it all gets too samey.
Wish I could sing though.