Im not going to debate this too much. Ive been playing MM basses for a while now, and loving how they play, but never quite finding the tone to match my hands. Too much lows, not enough highs. Barky mids that were to brash for 1/2 of the situations i play in.
I recently picked up a Fender Jazz MIJ, and have not been able to put it down.
My vote leans towards fender, as first and foremost they created the electric bass. That makes them the most copied bass design out there. As such, they also have the most aftermarket parts available to them, which can consistantly be found at ANY music store.
My pickups go out? 3 stores have them in stock. My MM pickup breaks, i have to send it into the company and wait for them to ship me back a pickup i paid for. G&L has non-standard parts as well.
That being said, i find that for me, my hands, my amp.. its going to be Fender from here on out. I'll still have a few flavors of MM basses (HH 5, HH 4, Sterling 4), but...
My primary instrument is no longer a $1400 Musicman. its a $500 MIJ Jazz.