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I've been eyeballing several wide angle lenses for a while now and I'm slowly getting closer to purchasing one...

I've narrowed it down to:
-Canon 10-22mm
-Tokina 11-16mm

I can't choose... I've heard the Tokina is sharper but the Canon is wider.. and I would be mainly shooting landscape/ architecture so the extra width could really help.. What do you guys think? And also whats the gripe about buying used lenses? Do you guys recommend it at all? I'm assuming that if I find one in mint condition, it wouldn't be a problem. Thanks in advance.