Not disagreeing with you because Anelka was effin' unbelievable, but Diaby was one of the best attention to detail type of players I've watched. He was also an extremely underrated dribbler and was a brilliant playmaker. I think I would take Anelka, but not sure if it's easily.
I really like this question, tough because each provided an excellent form of strength to their respected club. Hamsik is more underrated, while Isco is the more exposed since he got to play for Real. Hamsik is the better goalscoer, Isco is the better playmaker. Holy smokes, damn the more I am thinking about it the more either player would be useful depending on the situation. Like if you put Hamsik in Isco's position for Real and the Spanish national team would he have been more product? Likewise with Isco? Would he have made Slovakia better? Super close, but I am going with Hamsik, harder to score goals from the midfield.
Nemanja Vidic vs Vincent Kompany?