Two up

Double surfskis

A double is not a single with a second hole in it. The hull carries roughly twice the load, the trim depends on how that load is distributed between the seats, and the boat's manners depend more on the crew's timing than on either paddler's individual skill.

The paddler weight figures here are per seat. A crew's combined weight is roughly double the design figure, and a badly matched pair, one heavy and one light, sits the boat down at one end and takes stability off both of them.

Doubles reward practice together far more than singles reward practice alone. If you are choosing between two, choose the one you can borrow for a season.