1) waterproof spec and 2) battery life.

I've had DSC VHF's (not handheld) for over the last 12 years. I've heard THREE distress calls (all apparently not really emergencies). I'd save that for your base station. If you need to call for help, your mobile will give only slightly better distance than waving your arms :^).

We have an ICOM mobile with one of the best rated battery reserve capacity for a handheld.

http://www.icomamerica.com/en/products/marine/handhelds/m88/default.aspx