Community: These are roughly equivalent. The Rails community is probably significantly larger, but there's more than enough activity and information coming from both to keep you plenty satisfied.
Jobs: It's easier to find a Rails job.
Scalability: You can scale both. Both frameworks are pretty heavyweight, but they're also both designed with scaling in mind (e.g. decent caching is built in).
Fun: If you like CakePHP, then assuming you don't just irrationally hate Python or Ruby you should feel right at home with either one.
Full disclosure: I do Rails for a living.