UI framework choice

Hello, I need to develop a Rails application and to choose one framework for the user interface. These are my thoughts about the possible choices

1. jquery + one css framework (blueprint, Yui css, tripoli, ...)    pros        I have already used jquery and blueprint        open source licenses        jrails (rails plugin for integration with jquery)    cons        a standard library doesn't exist (jquery UI is starting)        there are many choices for the some widget (for example there are more than 4 tree widgets, which one should I choose)        widgets look & feel are different

2. Yahoo UI    pros        big company behind        open source license        coherent look & feel        one library    cons        integration with rails?

3. extjs    pros        more advanced widgets        one library        coherent look & feel    cons        license? (I need to investigate more)        integration with rails?

Any other suggestion or thought?

thanks .Stefano