So i'm asking the question that has been asked over and over before. Which lens should I purchase? I already have a 50mm f/1.4 for low light. And the AF on my 17-85mm doesn't work anymore, it was a decent walk around lens but image quality was mediocre. There is a 24-70mm for around $1100 on my local craigslist and a 24-105mm for $850. Is the 2.8 aperture better than the IS?