It's the best way to go unless you have specific needs.
For instance some insides only come in bunk bed layout(ask it's only on some ships). If you have trouble with stairs it can be easier to pay a few bucks more and get a high deck, or just avoid the need to take an elevator from 2 until 15 constantly. Some people go to the formal dining room for breakfast, lunch, and dinner and like to pick a room nearby. If you have a problem with sea sickness a low deck(2 or 3) midship is best. If your a light sleeper don't select a deck right below the pool or near the galley.
Personally I always take gaurantee unless it's basically the same price when I'll take the highest deck possible. This makes it easy to get to the pool/fitness center/spa, and everything else is down where I can take stairs at least one way.
11 cruises in 2012, 90 nights at sea visiting 15 countries
8 cruises in 2013, 56 nights at sea visiting 7 countries
Next cruise: None scheduled
PM me if you need a cruisemate for any Europe, transatlantic, or Panama Canal cruises
Date, ship, cost pp