RIB/Hardboat - Hardboat by miles
O2 - You even need to ask?
Onboard Compressor (free fills or happy to pay) - Would be nice, saves bringing 2 cylinders etc.
Teas/Coffees (on tap or limited) - Must have hot chocolate as well
Snacks -
Jaffa Cakes Speed (planing hull or non planing) - Quick is good, but stable is better
Diver Lift - Depends on the diving, but always VERY useful
Deck Area - Bigger the better
Shelter - Enough for all (even if it is a squeeze)
Toilet - Yes, with working lights
Kitting up Bench - Essential
Emergency Cylinder & Reg on line. - Upto divers and dependent on their plans/methods
Dry Access & Egress from boat - Doesn't bother me
On board storage (overnight) - Ditto
Overnight tank fill service - Nice for those weekend trips
Basic scuba spares for sale (eg masks,o'rings, fin straps, goodie bags,batteries etc) sale or borrow, there must be bits left on boats all the time
fresh water washdown (deck shower/hose) - Not essential
A decent list of marks is always handy, as is a skipper who can hit them.