Which Pattern Should You Choose?
All three of the patterns are good designs, so which you choose for your reengineering project depends on the target UI. If you want to build a browser-based web application, MVC is the best pattern to choose. ASP.NET MVC is designed around the MVC architecture, making new development and reengineering easier and faster.
If you want to reengineer a Winforms application, MVP is the best choice because it simplifies testing by consolidating event handling. Because MVP puts binding logic in the presenter, it also enables more testing because the model binding logic (indeed, any logic) in the view is untestable.
Finally, if you want to reengineer to either WPF or Silverlight, MVVM is the best choice because it takes advantage of the strengths of WPF command binding and other features, greatly enhancing testability of the application.