I did a spray tan (Mystic Tan) for my brothers wedding and it was a holy disaster. Seriously. Like DivingPrincessE said, it takes some time figuring out your angles because I had streaks and spots like it was no one's business, and it is looked ridiculous. What I ended up doing was taking a lot of showers, baths, pool sessions, etc. before the wedding to try and get it to wash away. And, it works, especially when I used a washcloth to, essentially, exfoliate the top layer (dyed layer) of skin off. Needless to say, I won't do it again.
If you are new to it, you might just wish to pay a bit more and actually have someone airbrush the tanner onto you. However, this will have the same limitations - it will come off faster because of the water, wetsuits, gear rubbing, etc. And, unfortunately, you will look a bit "leopardy" because it won't wear off in any uniform manner.
Otherwise, I've heard wonderful things about the self-tanning lotions and SELF magazine recently rated Nivea's (with skin toning - bonus!) as being one of the best, if I am remembering correctly. The great thing about these lotions is that YOU control the amount of color you get, its more gradual and - best yet - you can take it with you on your holiday and "touch up." I am going to start using it for an upcoming trip I have planned.
Best of luck.