It has to be coldbox really.
It has excellent documentation on the site, and also has a book which has been brilliantly written to cover many aspects about object orientated programming, amongst other topics. Honestly, really impressed by the book, more than I was expecting.
What I like about the framework is that it uses coldfusion code in its handlers, when I picked it up I think the other frameworks where using xml...not sure if this has changed.
The framework is easy to pick up if you are knowledgeable on CFCs, and has several useful features for building sites. PLugins, Debug toolbar, URL rooting for "pretty URLS"..
I cant speak highly enough of the framework..
Theres also a really helpful community here who respond to all my questions really promptly.