The Java Foundations 1Z0-811 exam is priced lower but don’t let that fool you. It is still a valid certification credential. If you've taken Java Foundations training or the Java Coding and Concepts MOOC this is a great place to start.
If you've attended the Java Fundamentals training and had some hands on experience then the Java SE 8 Programmer I 1Z0-808 exam is a good choice.
The difference between the Junior Associate and the Associate certification credential is experience. Take the Junior Associate if you haven’t gotten that needed experience yet.
First thing to do is to review Exam Topics. This gives you a detailed list on what you will be tested on. After reviewing the list you can determine what kind and how much additional help you need to prepare.
Hope you found this helpful!