Omar is tied for third in all-time Fielding Win Shares for shortstops with Hall of Famer Rabbit Maranville. Rabbit does, however, have 20 more overall Win Shares than Vizquel. Other than Omar, three of the top ten defensive shortstops are not in the Hall of the Fame—Dahlen (again!), and Dave Concepcion and Tommy Corcoran who finished with 269 and 214 total career Win Shares, respectively.
In the Wall Street Journal, Jared Diamond discusses Omar along with other Hall of Fame candidates. We provided some of the same research as in this Stat of the Week. Just a point of clarification, the article quotes me as saying that the data suggests that no more than 15 or 20% of a player's total worth derives from defense. However, what I meant was that defense as a whole, compared with hitting AND pitching is worth 15 to 20% as part of the game overall. Defense, as part of an individual position player's value, would be higher than 15-20% on average because he doesn't pitch. For a shortstop or a catcher, a player's value as a defender could be as high as 40% of his total worth.
About Win Shares: Developed by Bill James to assess a player's value to his team, one Win Share is set equal to one-third of a win. If you add up all the wins a team has, the team Win Share total is exactly three times that number. A player's hitting, fielding, and pitching performance are each taken as a separate component of Win Shares, the sum of which is his overall Win Shares total.