Tokina 11-16mm f/2.8 is a beast on full frame. Here it is around 16mm: still vignetting at the corners- but look at the view!
The price is pretty good though- $600 for the Tokina versus the $2400 it would cost for the Canon 14mm (however, it is aspherical – no distortions! or at least as clean as you can get for being so wide). So either I need to win the lottery, or find me a sugar daddy.. hmm.. both highly unlikely. Darn.
Anyway, I’d have to say my go-to lens for just exploring has to be my Sigma 50mm f/1.4 — see below