UI framework choice

Rails
1

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