Well... rent both of them and take them out for a walk then see which one you like best, and get that one.
Anyway, what type of focus issue are you talking abt? Sure Sigma's quality control is serioulsy lacking, but all you need to do is do a thorough check before purchasing the lens. It should be alright. There are heaps of people swearing by their Sigma 30mm f1.4.
(Btw... I am using a 28mm f2.8 which I find pretty alright in term of sharpness and stuff).