Anything water proof and has a search feature is nice.
A weatherband button to easily get the weather is good too.
The big thing is that VHF is line of sight.
So don't go with a short antenna.
And try to get the highest db rated antenna.
And don't get a plastic mount.
I always go with a stainless steel mount instead of that cheap cast chrome metal stuff.
More money but the antenna is safe.
And a good ground is really important.
If you have an aluminum boat, you're ok.
If it's glass, be sure to run a ground wire from the back side of the mounted under the fiberglass back to the negative terminal on your battery or a ground point in your electrical system.
The antennas are what they call a ground plane device and the ground helps to get the strongest signal possible.
Lastly, hand held units are ok in the harbor or very close to shore but have very limited range.
Good luck.
Mac