REST vs. SOAP可以获得大量具有安全性的数据

I have a requirement where I have large amount of data(in form of pdf,images,doc files) on server which will be distributed to many users. I want to pull these file using web services along with their meta-data. I will be getting the files in bytes. I am confused in which type of web service will be more secure, easy to parse? Which one is easy to implement on iPhone client?I have a requirement where I have large amount