Vems,
I have just passed Air Law (last Saturday). Human factors are next, as recommended by the Examiner. He recommended this one because I haven't yet started my instructional flying (like you I have done some with friends). So Human factors is a nice and easy one to get out of the way.
Remember you have 12 months to pass all of your exams after your first pass, then 24 months after your last pass to take your practical skills test.
A good bit of advice for someone who hasn't sat any exams yet would be not to rely on the confuser for knowing the entire question bank. I knew the entire 180 questions and could answer the question without fully reading the question, which is bad because in the exam it is completely different. So swat up on the AFE PPL2 or Pooleys Air Law book. Then goto the confuser.
I would imagine Nav and Met would be easier to pass once you have subconsciously absorbed information when you are further into your training.