In one way you can argue that Bud Harrelson is the most successful New York Met of all time. Harrelson was a member of the Miracle Mets World Series Championship Team in 1969 and was a Coach on the 1986 World Series Champions too. This makes him the only Met to have two World Series rings who was once a player.
Harrelson was not a hitting star (he actually made fun of his lack of playing skills) but was a defensive gem. The Shortstop would win a Gold Glove in 1971, a season where the voters got it right as he would lead all fielders in Defensive bWAR. From the strength of his glove and his high profile with the Mets he was named to two All Stars.