still haven't found out what makes a comfortable neck for me... I would love if some day I could buy a bass purely based on it's data (nut width, shallow or not so much etc.) but that day will probably never come. One thing I have learned is, that a proper setup and good strings can really work wonders, and sometimes turn an unplayable bass/neck completely around. The other thing I've learned is that string spacing is extremely important for me... 19 mm. is juuuuust right.
Best/fastest necks I've encountered so far:
Elrick Gold NJS 5 String
Tune 5 string (don't recall the model... It's almost 20 years ago)
Warwick Dolphin NT 5
Still long for an Elrick, and if I see one on the market sometime, at a reasonable price I will fight you for it .
Had a few 4/6 stringers with good necks, but comparing them to the 5's would be unreasonable... 5 Strings is definately my main instrument, although I would like a 4 string 'slapper' at some point