For me it's a hard choice between Arteta, Cahill and Seamus.
Arteta was £2m, our best player, gave us the best years of his career, and then was sold for £10 million.
Cahill was £1.5m, a fantastic player who really 'got' Everton, and left on good terms for £1m.
Seamus cost 60k, has become one of the best RB in the league, is rightfully being touted as a potential captain, and if sold would command a significant fee.
Gone for Coleman just because of the outstanding value and potential to be an even better buy than he already is.
Honourable mentions for Pienaar, Jags, Baines and Pienaar. Got to give Moyes his dues, was incredible in the transfer market.