Would highly recommend this small book on “The differences of the four imams”. It clarifies a lot of important issues and walks you through the reasons for why difference of opinions exist.

One of the most powerful illustrations comes right at the beginning where he lists various reasons for why there are different versions of the same Hadith which appear contradictory, then concludes that only someone with sufficient knowledge can ever decipher the rulings from them. Sheikh Zakariyah Kandahlawi then proceeds to lay out a powerful argument behind the necessity of following a credible jurist who is able to navigate the Hadith literature, giving examples of single authentic (sahih) hadiths which alone can be misleading if the context and wider understanding is not given along side it. He then continues to discuss how legitimate difference of opinions emerged surrounding the same issues, citing examples of how imams differed based on their methodology of analysis within their school. All this is done in an easy-to-read, simple yet effective manner.

You can buy it at: http://www.ghazalibookstore.com/differences-of-the-imams-new-edition-p-1564.html

PDF Download (though I have not read this version):
http://attahawi.files.wordpress.com/2010/10/differences-of-the-imams-shaykh-zakariyya-al-kandhlawi.pdf