The more I read up on the different frameworks the more reasons I find that people prefer one over another: ease of development; speed and scalability; plug-in architecture and add-on features; quality of documentation… All of it matters, but some, I think, much less: yes, it’s troublesome if a framework has poor documentation and is difficult to development in, but I think the length and slope of the learning curve is especially significant in conjunction with the results of mastery: a violin, for example, is one of the hardest musical instruments to learn, but once mastered, its potential far outstrips almost every other instrument.
Assuming a baseline of functionality – an object-relational mapping to the database, a reliable MVC structure, an authentication class, et cetera – and assuming a baseline of accessibility, where the documentation is detailed at least enough to allow mastery of a framework within a reasonable period of study, I think that frameworks should be evaluated on their maximum potential. A framework should be extensible, transparent, and professional.