Omar Vizquel. No one I've ever seen was on his level. He was automatic.
That was my thought as well. Though, I feel like there was about a five-year period where Rey Ordonez was as good as Omar or Ozzie or anyone. He didn't have the longevity, of course. But for that peak...he was something else.
Also, Keith Hernandez, I had the pleasure of seeing the end of his career. He was amazing, as far as 1B go. Great range, and man could he pick them. The Metsies also had John Olerud who was an all-time great with the glove, IMO.
That whole Mets infield of Ventura, Ordonez, Alfonzo, and Olerud grades out by many metrics as being the best-ever defensively.