I'm still thinking about buying my first fretless and still torned between a Yamaha BBN4F and a MIM Fender Jazz. The possible upgrades on a MIM make me think it could be the right choice. But it seems that a lot of MIM owners have tried several ones before buying. So, how many have you tried ? How do you recognize the "good" ones ? No dead spots ? Where are they generally ? No hum ? ???