Hi Manuel,
First of all. Welcome to JavaRanch !
I think my experience would be helpful for you.
Well, I purchased both Sun ePractice Exam and WhizLabs Exam.
I personally found WhizLabs better then Sun one.
As you said, Sun ePractice exams doesn't contain drag n drop questions and you also have to have a web connection in order to see and answer the questions.
Don't forget that Sun ePractice exam also expires after a few months whereas WhizLabs does not.
If I was you, I would go for WhizLabs Exams, for sure you will threasure each cent you would pay for it.
I also would like to say that WhizLabs Exam comes with a VERY GOOOD "Revision Notes" that you can use to remember key points before during your study journey.
Of course you are studying aiming pass the exam, but keep in mind that if you don't, WhizLabs will refund all amount you spend. Do you see as buying WhizLabs is a NO RISK choice ?
Concerning the scores, please read careful the link above provided by JSato. I put some comments there that can help you a lot.
I also recommend you to take a look
here. I post my experience and some tips for those who are preparing for SCJP exam.
Good luck man.