OK, long answer for you....
Start with something of 5 million pixels or more, that'll give you good quality A4 prints. More pixels are better, you'll be able to crop and still retain a good pixel count, but I'd avoid the latest headline grabbers as the higher the pixel count the more noise you get on pictures taken at anything but the lowest ISO setting. Current top of the range seems to be 10 million pixels, so I'd suggest you go for a camera with 6-8million pixels.
Extended ISO ranges are a decent feature. Most compacts have a minimum ISO of around 50 to 100, but the top setting is increasing steadily, with some now offering upto 3200 ISO. In practice, the higher the ISO the lower the light in which you can get pictures but the trade-off is increased noise and reduced picture quality.
Next, take a look at housings. If you want to develop your photography you'll need a housing that will take add-on lenses for wide-angle and macro shots, so make sure the one you buy will take them. All the Oly housings do, with a 67mm or 46mm screw thread. The 67mm ones are probably better as you can get a slightly wider range of lenses for them. If you want to avoid Oly then check the Inon lists of the housings for which they make adapters. Going this route also means you have access to Inon bayonet fit adapters and they're much quicker and easier to use underwater than screw fits. (
Welcome to Inon America)
Also consider your depth requirement - if you're happy with 40m the manufacturers housings will be good - and cheap - if you want to go deeper then you'll need an Ikelite housing, so check their list (
IKELITE Underwater Systems), or a Sea and Sea outfit (UK distributor Aklan James,
Alan James - For all you need in underwater photography). A good UK dealer for all of these is
Cameras Underwater Homepage: Underwater housings, digital stills and video cameras, accessories. Gates, Ikelite, Epoque, SLR, DSLR, Sealife, Sea&Sea. .
From your question you want an easy to use all-auto camera - the good news is that they all are, you just need to select the auto-everything mode on the camera and you're set. When you're ready you'll want to use other modes as well, aperture priority and full manual control. Forget the ever increasing list of 'scene modes' boasted by many new cameras, they're pretty largely an irrelevance and you can duplicate any of them with aperture priority or manual mode used properly.
Macro is also easy, most cameras offer macro settings built-in, but a better way to go is an external macro lens. Built-in macro usually defaults the camera lens to the wide-angle position, meaning you have to get really close to your subject. Using an external macro lens reduces the maximum distance on which the lens can focus from infinity to a much shorter distance, something like six to eight inches, but allows you to use the camera zoom. That means you can get good macro shots with the camera a bit further away so you have room for extra light. Start with the in-camera macro setting and the built-in flash, then go to the macro lens and an external flash when you're ready.
External flash is also easy, there are a variety of small external strobes available that will work with any digital compact.
Finally, consider a camera offering RAW mode file storage. I'm not a huge fan of RAW for routine use, but in tricky conditions it can be a picture saver.
For me, then, I'd recommend something with 8 million pixels, full manual control and a housing that will take accessory lenses. Brand doesn't matter, the pics will be near as dammit identical regardless of maker, as long as the camera met those criteria.
As ever, all my opinions!