I think the point and shoot is the way to go. They are smaller and trivial to transport with you at all times. You never have the issue of bringing the camera and leaving the housing, only to find out you are going to get wet. Being a spare camera, if you drop it into the drink too deep to dive for, you still have another camera on hand for the rest of the trip.
I have a Panasonic Lumix DMC-TS3. I think it takes respectable pictures for being a point and shoot. The GPS function is nifty, though it is fairly slow to update. I have several pictures from out of state that are tagged with my home location despite being 500 miles away. You can tell it to reposition, but it doesn't really offer any info on its progress until eventually it just updates without any notice. I picked it because it had the best advertised speed for startup and shutter lag.
Whatever you do, if you're in the ocean, you'll need to lug around a nalgene or something else full of fresh water when you go snorkeling, to rinse off the camera when you get out of the water. Salt water seems to destroy the seals in many of the cameras. I formerly had the Olympus Tough 790, and I brought it on a cruise, I never rinsed it off, and after sitting in my swim gear wet for hours, the seals went bad and the camera was ruined. The LCD display failed, but was able to continue taking pictures with my best guess for framing, so it wasn't a total loss for the vacation. After reading online, I see that is common for a lot of the underwater point and shoots.
Here are some sample pictures with the DMC-TS3, here is a friend in a waterfall:
I tried to take a picture in the waterfall, not much to see, but its obvious I'm fine getting it wet!
Two images out of the water.
All images were reduced from 4000x3000 to 2000x1500 for upload.