Or just buy a quiver of 2 Gongs for the price of one major brand board ... Sorry for the pimping, couldn't resist :-).
On a more serious note, it depends a lot of the type of surfing you want to do: (I will take examples in the Naish line)
- Longboard style: you can noseride but need to move a lot fore/aft on the board. In the Naish line, the Nalu
- Cruising style: pointier tail & nose, but with a fast rocker (unlike the Naish Hokuas) to be fun in weak waves, you draw cool curves from the middle of the board. I dont think Naish have one, it would be an Hokua with a flat rocker.
- Fish style, a bit like a longboard but more front rocker, pointier nose, and a wide tail so you can put your foot on the fins for radical turns even on weak waves. For Naish, the Mana seem to fit the description.
- Hybrid: the front of a race board and rails and tail of a surfboard. PSH Hulls, Gong Perv, ...
There are other styles, but these are the ones I can think of that can be compromises between surf & flat.
You can find these kind of boards in most brands, but I would avoid the boards designed for Hawaiian waves, they have too much rocker for places with no "regular waves"
For flat water, length is the key. Some slight convex/belly in the nose can help. I would stay longer than 9'6". Wider is slower, so avoid the whooper for instance. Parallel rails have less row (the Fish or longboard style, or even better, the Simmons). Pointed noses are more fun in chop.