If you want the safest possible option and the only one where the resort has liability beyond a minimal amount, you should have the front desk lock up your laptop in their safe deposit box. Even I don't do this, as it is somewhat inconvenient given that you have to actually go there and possibly wait in line to drop it off and pick it up.
The next best choice is to lock it in your room safe. Unfortunately, not all WDW room safes are large enough to accommodate a lap top so this is not always an option. I always do this if the safe is large enough.
Your next choice would be to secure your computer with a cable lock to something that can't easily be removed from the room and keep it out of sight. If the safe is not large enough, this is what I would do.
Moving down a level would be to hide the computer somewhere out of sight. I have done this in the past.
I personally would never just leave an unsecured (or even cable locked) lap top sitting out in plain sight. Most hotel room thefts are going to be crimes of opportunity perpetrated some ne'er-do-well walking by while mousekeeping has the door open, a sticky fingered mousekeeper or maintenance person, etc. and the thief is just looking for something they can grab in an instant. An expensive piece of hardware sitting out fits that bill to a "T." Of course people do it all the time and most of them never have a problem. I also lock my car even when it's in my driveway or garage, I lock my garage and I lock my house even when I'm home.
- they found it, wrapped it in bubble pack, and sent it home to me unharmed. 
