WYSIWYG recommendations for my Rails app

I'd suggest to use gem ckeditor it's really perfect solution, i used it recently in my Rails 3.2 project

A pretty cool and fancy one is Sir Trevor JS. There is also a gem

We use TinyMCE quite a bit.

No unbelievable feature set or anything, but it does have a nice jQuery integration plugin (which goes a long way for us).

The live preview functionality seems very doable.