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