You can use full-frame EF lenses on crop sensor cameras, but cannot use EF-S lenses on full-frame cameras.
I would suggest favoring getting EF mount lenses for a couple of reasons. One, they'll work on crop and full frame sensor cameras, so if you upgrade to say 5D/6D you won't have to buy new lenses. Two, crop sensor cameras use only the center of full-frame EF mount lenses, this is the sharpest part of the lens and you get very little (if any) light fall-off/vignetting, see here:
http://www.the-digital-picture.com/Canon-Lenses/Canon-Lens-Vignetting.aspxCaveats are the focal length changes using full frame lenses on crop sensor camera, must use multiplier (1.6 usually, some cameras 1.3) to determine new effective focal length. For example, a 35mm EF lens on 1.6x crop sensor camera would effectively be 56mm. Also, EF mount lenses are usually bigger/heavier (for primes, not really an issue, for zooms it can be) and more expensive.