When runway is damp and no braking coefficient given,if your Airline/Authority doesnt provide you guidance,I would use dry perf if familiar with airport,runway condition.
If you take off from an airport with unreliable
Information and/or a runway which tends to be slippery when wet( due to for example rubber deposits,poor runway consition..)the wet perf may be a better option in most cases.
Most airports which give damp,i have found the landing distance to be very close if not exactly as dry perf..