"Better by whose definition?
They buy what they want and need for the job at hand."
Well if you're asking who thinks the A330 MRTT is better than the KC767, then I do for starters.
More fuel to offload. More freight capacity. More passengers. Simultaneously. Better field performance. More modern boom system. Systems proven on the A310 MRTT now in service with the Luftwaffe.
BETTER, in other words.....