Had a quick play with a friends copy of the 10-18mm at the weekend and previously owner the 10-22mm myself. I would say on balance go for the 10-18. Its a lot cheaper (£300 vs about £430 for 10-22 with current rebate) and takes photos that are at least as good if not better and benefits from IS. The only reasons to go with the 10-22 is if you already have it, prefer the USM motor over the STM motor in 10-18 (there is no direct connection between the lens focus ring and the lens its all electronic in the 10-18), really need the slight advantage in aperture speed f4.5-5.6 vs f3.5-4.5 (but without IS), or have a fetish about lenses with yellow rings on them. When I used my 10-22 it was almost always at the wider end so doubt you will miss the 18-22mm range
Oh and the 10-18 is also a lot smaller and lighter which helps when carrying it and using it at its widest with an flash (the 10-22 left a big shadow when using most on camera flashes due to its size)
