I'm thinking about taking up flying and have found a few schools in the US
that seem quite resonable (for price and facilities). They offer several
courses - i've narrowed it down to two: 'PPL Private Pilot License' and
'CAA/JAA Private Pilot License'. Can someone tell me what the difference
between the two types of license is? I've had a good rake around and can't
seem to find anything!

CAA/JAA is the European curiculum.
You need that if you're a European citizen and want to be able to fly a
European registered aircraft at any time.
If you're not an EU citizen an FAA PPL is enough, which is a lot easier to
get (the European guidelines are far stricter, as is the medical).

I would like to at some point get a night and IMC rating so with this is
mind does anyone have any suggestions on what I should go for (license
wise)?

You always start out with PPL. After that you can do extra training (and
exams) for night and IFR ratings, multi-engine rating, etc. etc.


Lastly, there are several aircraft to choose from on each course: Cessna
152, Cessna 172 and Piper PA28. Does anyone have any recommendations for
choosing an aircraft for learning to fly in?

Doesn't matter much, except for cost (152 being cheapest, Pipers usually the
most expensive).
I find 152s too small (I'm rather large) and cramped.

Finding a school that has well maintained aircraft AND good instructors is
more important that finding one that has fancy aircraft.