I have to say, It's so cool to see some of these answers. While there are so many remarkable instruments in this thread - from well worn warrior battle axes to incredibly high works of art - the thing that I like best are the expressions of endearment that are just as deep regardless of the price, rarity or commonness of the instrument.
It just goes to show that it's the player and the player's heart that makes the musician, and the instrument in all of its ragged or refined glory is a reflection of the artist or roustabout who wields it and gives it value.
The basses I use are few - only 4 in my possession - only 2 in working order, which, of the working, only one belongs to me.
The favorite is a 1978 Rickenbacker 4001 Azureglo. It's been in my safe keeping for a friend for about 15 years. Bought used. A repaired snapped head stock. A bit of a dog as R.I.C.s go. But it's seen so many great jams, been played by so many great people - It's worked in some very cool bands, made some recordings that I'm privileged to be a part of - has been around the globe - and it belongs to one of my most long standing friends, known for over 40 years. It's the instrument that has made it possible to be playing in the role as bassist.
I'm not one to change instruments like shoes. Nor am I one to buy/sell/trade - once I get something, it's forever part of my box of paints. I meet it, get acquainted, explore its secrets, and make peace with its imperfections and embrace it for its own character and voice - then engage in the ongoing conversation.
My Ovation Celebrity CC174 acoustic is one of those goofy things that I'm enjoying meeting it where it's at. It makes me think and play differently and is really great to just pick up and play for quiet unplugged spontaneous rehearsal. It has its own vibe and I like it.
I have a little in-need-of-help Gretsch Electromatic short scale that has yet to run, but I'll welcome its quirks, too. -- Lastly, my Frankenbass Lotus/Warmoth fretless is something I'm excited about - whenever it returns from the luthier. I'm trusting that'll be a whole new beast to commune with. I can't wait to start that conversation.
Point being, they're all different and they're all special, and I look forward to the next phase of several possible musics evoked by all of them, mostly because they'll connect me more with the people and craft of music that I care about and identify with as my interface with life.