Best tanker? Easy really, he's the fellow who comes to get you when you've pushed the fuel to stay on task for that extra couple (or so, gusting 20) minutes to get the job done....it's very humbling indeed to hear that there's no more gas in theatre but 'random callsign 12 is hauling the mail up the boulevard to try to get to you'.
Let's not forget the C2 fellows who give you the snap to the tex when your BPM is in the low two hundreds. Absolute gentlemen.
Worst tanker? No such thing. From Transall to Extender, they're all, genuinely, my heroes.