Aluminum, As well as the points made earlier, aluminum will take less motor to power the boat. This will keep cost down or you may be able to afford the highest performing motor the boat will allow. I have a crestliner phantom v170 sport fish. It is welded aluminum. Its a 1989 year boat has a 2004 75hp 4 stroke (second motor on this boat) it is tight as a drum, solid as a rock. As far a beaching, most aluminum V's are painted and that may scratch your paint, I would suggest a keel guard only to protect the paint.
In 1980 my Dad bought a 1962 Starcraft Chieftain. This boat came out of the Tampa area in Fl. and ran exclusively in salt water and it was a riveted cruiser. It was so funny that the cockpit looked like the cockpit in a boeing 727 as this boat had outlived 5 motors. Each time a motor was replaced guages were just added to, so there were multiple tacks, key switches, altinator guages and so on. This boat was in a slip and would only have to be pumped out after a heavy rain. Was sold in 1996 and is in VA. now. I can vouch that aluminum is durable.