Which validation framework would you prefer for a webforms application. This would be for a rather large complex app. I would want to specify rulesets and business validation in a single place and integrate it both on the client and server side. I'd prefer jquery for client side.
Anyone has any suggestions?
You can look at .NET 3.5 DataAnnotations. because it integrates well with ASP.NET, but I don't believe it supports the concepts of rule sets. Another option is Enterprise Library Validation Application Block, which supports custom rule sets, however, it will take you slightly more time to integrate that with ASP.NET. However there is online material that should give you a kick start. Here an article (written by myself) about integrating VAB with O/RM tools and here is an interesting article about integrating VAB with ASP.NET.
Good luck.