I would have to say my '76 4001. For several years in the early '90s, I was trying to live the dream with music in a Massachusetts band called Jiggle the Handle. We never made any money, though, so the entire time my workhorse was a Fender Japan '62 Jazz Bass reissue.
I remember that band, I don't think I ever saw you guys though, but that is a memorable name and your band got around if I remember right, I'm from Millbury, very close to Worcester. I was in school at the time and didn't get out very much.
I got very sick during the mid 90's and sold the love of my life which was a 68 Candy Apple Red P bass with a 66 J neck on it. I owned it for 18 years and was my primary bass all that time. I had a fretless neck on it for a while, but went back to the J neck. It was originally a rosewood fretless.
I have several basses now and go back and forth over which is my favorite, among them a mapleglo 79 4001, a black 72 fretless P bass and a sunburst 2007 Gibson Thunderbird. I also have a 72 jetglo 4001FL but I don't play it often and a 69 EB-3, they'll have thier tu=imes though I'm sure.
I actually think my SVT's are the real loves of my life though. I can change basses and really become attached to them but can't change amps, I think it's something to do with bandmembers on fill in gigs automatically thinking you are going to be the loudest thing on earth and scowling before you even play a note.
Seriously though, it's the sound.