Best Wide Angle lens option for Canon 7D

----I am thinking of buying a wide angle lens for my 7D but the higher prices of canon L series are great disadvantage to me .So i am seeing the options like Sigma 10-20mm f4-5.6 EX DC HSM,Canon EF-S 10-22mm f/3.5-4.5 USM & Tokina 11-16/2.8 ATX DX . I have a EF-S18-55 mm with no IS which i am not satisfied.I have gone through many reviews but still cant figure out which will be the best wide angle.

Question:

1. Will there be any technical disadvantages to the camera due to third party lenses.

2. And lastly which lens should i invest for ??

Info :
My flickr profile: http://www.flickr.com/photos/rhivu_ray/
Use:I would use this photos for exhibition,contest and professional level.
With 7D i have EF-S 18-55 mm, EF-S 55-250mm IS-II, EF 50mm 1.8 - II

regards , Rhivu.