The A710IS but it is an older generation of camera with the Digic II processor. The A570IS has the newer Digic III processor which gives faster response times and additional options. Overall specs make the A570IS a superior camera, IMHO.
I have been shooting the A570IS on land for several months now and dove with it in June. It is a big step up from my old Canon S30 with Canon WP case. The focus speed is much faster, colors are improved, UW setting is good for starters, manual modes give great performance, IS feature is great on land and does have benefits underwater, and this is a sweet little camera. Another great feature is the ability to capture long videos with the A570IS. Get a big SD or SDHC card and you can almost take movies! (Well, not really, but it does capture nice clips upto 1-2 minutes.) The battery life is good but not fabulous since it uses just 2 AA batteries. Be sure to get 4 good 2700 milliamp batteries and a quick peak charger (Canon & Sony make a nice compact 4-AA charger). Considering this camera can be had for under $200 now (plus WP case), I think it is a fantastic deal.