[mattbrewsbytes]

I was a Senior level Java developer and I would suggest Rails. It has the object oriented-ness you are familiar with from Java and a rich set of libraries (gems) as well as a lot of documentation online (railscasts).

SaaS is essentially a CRUD application serving some specific need - Rails is good about letting you focus on what your are building (e.g. the house) and not spending enormous time on infrastructure (e.g. plumbing, wiring, etc.)

Edit: I agree with mattwritescode: it doesn't much matter which one you choose since they all will work. From my experience with Java though, you could spend a lot of time just getting infrastructure working - framework, JDBC, etc. Rails will have that out of the box (maybe Django too)