A wider view: Independent Super Wide-Angle lenses comparedBy Ben Boswell - Friday February 01 2013 Lens Review
This is not an exhaustive test, it reviews data only for independent lenses and the camera manufactures own offerings obviously need to be considered too. However, on the strength of the data available it seems that the best lens is Carl Zeiss’s Distagon T* 2.8/15. For a photographer who plans to use a super wide-angle extensively in their work this is the one to go for. Images straight from camera are going to be superior to those from other lenses. The majority of photographers will not be using a 14 or 15mm lens so much and so would probably be better off saving some money and buying a Samyang 14mm f2.8 IF ED UMC Aspherical. With the money they save they should also buy a copy of DxO Optics Pro 8 and a return ticket to somewhere to play with their new toy!