Quote Originally Posted by Soulburner View Post
Lower number, faster light travel through the lens. Lower is always better

It's basically like opening your eyes wider.
There are a few issues a large aperature.

1. Most lenses are a bit softer when wide open (lowest F number)
2. Possible vinneting in the cornerd when wide open (depens on lens and camera being used)
3. less depth of field (sometimes an issue and sometimes you want more)
4. lack of low depth of field with some lenses (primarly F2 and below) will sometimes cause focusing errors where the camera will either not be able to focus or will focus at the wrong point. This is generally a problem with cheaper lenses like Sigmas, but some of Nikon and Canons high end telphotos (70-200 F2.8) have known to been off a little on the focus.

Other than that, its generally better to have a wider aperature.