Easiest acceptance testing framework I've used is Splinter. It's an abstraction layer over Selenium that practically makes writing tests similar to plain English: http://splinter.cobrateam.info/
Admittedly, I only took a cursory look at Splinter, but in my opinion Robot Framework[1][2] is much closer to plain English. This can be good if you know what you're doing and can come up with consistent naming and test/keyword organization conventions, or bad if used by someone without basic understanding of a concept of a function, white space delimiters, etc.
Still, it is super flexible, and I enjoyed using is a lot. Nice feature is having executable requirements if BDD is used. I.e. you can implement keywords to execute given-when-then req's and they became your test.
Lots of good options in the space of 'friendly' wrappers around Selenium.
For .NET users, FluentAutomation (http://fluent.stirno.com/) is a good option. Works in regular tests or with scriptcs .csx files. Can automate any of the Se supported browsers, including PhantomJS very easily with short, readable commands.
Absolutely love splinter! That being said, I implemented frame buffer support for both Firefox and chrome driver (for Linux clients) and saw phantomjs as unnecessary as a result.
Still, it is super flexible, and I enjoyed using is a lot. Nice feature is having executable requirements if BDD is used. I.e. you can implement keywords to execute given-when-then req's and they became your test.
[1](http://robotframework.org/) [2](http://code.google.com/p/robotframework/)