As Sonny notes, a credit card is a lot easier as far as removing hassles from your cruise. Having to give them a cash deposit, and then stand in a REAL LONG line to settle your account on debarkation morning can really take the shine off the cruise.
I use my Discover Card for cruises. A nice thing is the rebates they give based on use. For instance, I just deposited $100 to my bank account from the Discover Card rebates. This is money they gave me, essentially, since I carry no balance with them. The gasoline rebate is also a great deal.
You can set limits on a credit card. If they give you a high limit, just call them up and say you want X dollars as a limit. That way you can't get in trouble.