These are VLF machines so they are very sensative to wet salt conditions.All of them are good all round machines but you will have varying success depending on the composition of sand at your beach if you are planning to detect on the wet sand.
You will find detectorists who will tell you that they use all of them on the wet but it depends on the conditions and how far you have to lower the sensitivity (which will decrease detection depth). Some guys/gals don't mind falsing but personally it drives me nuts.
Some have reported good results using Technetics G2 and T2 (same detector as Fisher F75). But it think you should try and get someone in your area with one of these detectors to show you how it behaves under your local conditions.
As a side note, the AT pro is waterproof but then again I only see it as a real atvange if you plan on detecting in fresh water.
From experience I can tell you that the X-Terra (one of my favourite detectors) can detect 100% in the wet sand and in the surf on one of my local beaches but on another beach for instance you can't go near the wet sand or it will false like crazy.
Most detectorists will tell you that there is no one detector that excells in all areas. (The CTX comes close though
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