This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
If you have trouble choosing between the two, analyze your application and find out what kind of operations you're doing on your list. Choose the implementation that does the most frequently used operations the most efficiently.
First, a bit of business: you may not have read our naming policy on the way in. It requires that you use a full, real (sounding) first and last name for your display name. A single name isn't enough. You can change your display name here. Thanks!
Second, this is a beginner question, not an advanced one; I'm moving this thread to Java in General (Beginner) for any follow-up.