I use Canon 28/1.8 and 20/2.8... and am happy with them on my crop cameras.
24/2.8 and 35/2 are not USM lenses and are a notch below the above lenses in overall build quality. Shame, really, since I'd like to have a 24mm and 35mm, but not really ready to go all the way to the 24L and 35L (probably will end up with the latter, though. These are not important focal lengths to me on my crop sensor cameras, but are two focal lengths I like a lot on full frame, so became more important to me when I added a 5DII to my kit a couple years ago.
USA or Imported only matters if you ever need to make a warranty claim. The USA will be covered by Canon. The Imported lens won't be... you'll have to send it to B&H (in this case).
Heck, I've bought several lenses that were refurbished and more than a few used lenses. Refurbs usually have a short warranty. Used lenses might if bought from a dealer... But usually won't have any sort of warranty if bought from a private party.