A lot depends on your budget. I like the CZ-20 or newer 21 as it is the water version of the Fisher CZ-6a. The CZ-21 is kind of pricey and the reason I picked this one was because you wanted it for land hunting too. For land you need pinpoint other wise I'd suggest a 1280 which is half the price.
Another good one for land and water is the Tesoro Tiger Shark. The AT Pro is still having problems with, well you name it. Don't get me wrong, I have one, but it is not my "Go to Detector."
Many water waders also use detector that have a long coil cable and carry the box from a strap around their neck. One of these is the CZ-6a and 1235. You can change coils on these which you can't do on dedicated water machine.