There is definitely a difference between greatest Met and favorite Met, at least to me. Seaver is the greatest Met, the face of the franchise.
For favorite, I go with some one that likable, fun to watch, a supportive, hustling player. No question, Juan Soto is the best current player on the Mets, but he is far from my favorite current Met.
My favorite Mets would be David Wright, Francisco Lindor, Mookie Wilson, Rusty Staub & Brandon Nimmo.