I don't have one, or have any opinion on it, but Sigma has a 12-24mm full-frame f/4 Art series lens. The art series tends to be quite good, and it offers a different focal range than anything else suggested so far.

In terms of cost, it's right in the middle. Canon's 16-35mm F/4 is $1000, and the F/2.8 if $2000. Sigma is $1600 (Based on today's B&H prices).

Aside from the price difference, the other big difference is that it has a much wider wide angle. The the EF-S 10-22mm on crop is similar to the 16-35. The EF-S 10-18mm that you're used to would be equal to a full frame 16-28mm. 12-24mm would be a huge amount wider, and a touch shorter than what you're used to. If you find yourself wishing your 10-18mm lens could go wider, the Sigma would be worth further investigation. If you find yourself wishing the 10-18mm could go longer, then perhaps the Canon fits your style better.