which board is the best to buy?

Depends on where you live. Also, if your friend surfs, you should ask first. Worst thing you could is buy someone a board they do not like and expect them to surf on it. Search the net or look at some previous about top boards.

You should definitely try to find out what your friend likes. In general, fishes have become extremely popular due to the shape is ability to catch waves and paddle well while still being very maneuverable. Check out 9:Fish Surfboards at http://9fishsurf.com. These guys are experts at fishes since that is all they do.