It is just an opinion of course, but it will be a while before JEE7 will really be used by corporations. There is also little study material/mock exams available for the not yet existing exam. I think it is a better idea to go for the 6. If you should find you need the 7 after all, you can always do the upgrade exam in the future.
Oracle Certified Professional: Java SE 6 Programmer
Oracle Certified Expert: Java EE 6 Web Component Developer
Oracle Certified Expert: Java EE 6 Enterprise JavaBeans Developer