[relaunched]

It truly depends on what you are looking to do. If you are tired of PHP and want to learn a new language, build it in RoR. If you are tired of CRUD apps and want to build something more complex, build it in PHP. If you just want to mentally stimulate yourself and learn new things, do both.

Figure out where you are and where you want to go. Then, take the shortest path between the two. Note: it might just be that you need to get lost, wandering through the woods for a while. If that's the case, go nutz and build something crazy in a language you've only heard of in passing in an HN thread.