Depends entirely on the collar AND the face under which it is perched. FIH is great for point, pinned, and club collars. Half Windsor is better for semi-spread collars. You guessed it: full Windsor for wider spread and cutaway collars. However, if you're wearing a wider spread and have a narrower, more rectangular face (like me), try the Shelby knot. The result is a very triangular knot with a narrow bottom end. Google for how to tie one. Also, if you like a beefier but longer know with point collars, try a Prince Albert. Experiment, find what you like, and go with it.
Since I have a long, narrow face, I do exactly this: I wear buttondown or spread collars and use a half-windsor or windsor knot. Usually I'd prefer an asymmetrical knot, though, and I'm not sure how to get one if the FIH doesn't fill the tie space. So I only use the FIH with beefier ties.
Will give the Prince Albert a try. Edited to include Prince Albert.