Typing this on my phone so I really can't go into detail.
Anyways should I go with an EF or EF-S lens for my next lens?
I've been interested in wide angle and fisheye but can't decide what to get. I ruled out the wide angle EF since it wouldn't actually by wide angle on my XSi. This leaves me with either a wide angle EF-S or Fisheye EF.
I was leaning towards EF since that's the lens format Canon will probably stick with in the future.
both of them are going to be the same on the wide end. equiv to a 16mm in a 35mm format. just being it is EF-S doesn't mean it is going to be equiv to a 10mm on a 35mm camera.
biggest thing with your camera I would say to worry about on the EF to EF-S question is are you going to get a full frame camera? if not no worries as crop cameras can take both (not counting the 10d) but if you plan on getting a 5D, 1D or 1Ds then you will need EF lenses.