Easy one - 75hp, no questions.
I had a 50hp on mine first time round, it was too small and struggled to plane the boat when fully loaded. When I upgraded I put a 60hp on, which was better but a fast cruise meant running the revs quite high.
Gordon Moore (Manic Moore) who has Enticer, has a 75hp Etec on his - and it is superb. The 4 strokes are quieter on tick over, but when running they are about the same. The 75hp Etec pushes the Warrior along effortlessly and is frugal on fuel.
If you cant find / get an Etec or want a 4 stroke then either a Suzuki or Honda in that order.
Hope that helps.
Adam