The 16:9 should give you 33% more pixels I believe.
The fisheye won't give you widescreen. If you want widescreen you will have to crop - and thus loose pixels. If you want full res widescreen the anamorphic is what you want. If you need a distorted image the fisheye would probably be better.
EDIT: The anamorphic or 16:9 lens doesn't give the camera any new pixels it just squeezes a widescreen image down in one direction to fit the cameras CCDs giving a 33% wider field of view horizontally. When you stretch this out so the proportions are correct you get a widescreen image. The fisheye gives you a wide angle in both the vertical and horizontal directions equally so you cannot stretch the footage out without causing everyone to look too wide.
fisheye will only distord the image to have a larger angle of view (very useful for extreme sports) while the anamorphic adapter won't really distord your image and if you want to shoot skateboarding or snowboarding etc... videos, DON'T buy an anamorphic because it too long to set up!