From a students perspective it may be better for you to go down the JAA PPL route. You will have the benefit when you go to do your ATPL exams of having covered the basic material during your PPL studies. The FAA licence is handy to have if you can afford it after the JAA PPL. The written exams are very straight forward, as you get the full question bank before sitting the exam, the flight test is slightly harder and I certainly felt I benefitted from it. You shouldnt need more than 10 hours in the worst case scenario.
I know that some people have come over and done the FAA licence first and on the back of that converted it to JAA, this has the benefit of letting you skip some of the exams bar Air Law and Navigation(?), but again if you are thinking of going all the way to Commercial its nice to have covered some of the subjects you will cover in the JAA PPL.
Another point to note, and I dont know how important it is or what difference it makes if any, is that on your JAA licence it will have words to the effect of "Issued on the basis of FAA licence". Now, if that might make a difference to anybody at any point I dont know.
Has that answered your question?