I had a Sigma 120-300. Not the current version, but the one before. I broke my vow to buy only Canon lenses. I wish I hadn't. I HATED that lens. It was sooooo slow at autofocusing. I eBay'ed it to some guy in South Africa and bought the Canon 300/2.8 IS II. I love the Canon. Maybe I'm just too picky about my glass, but I have regretted buying anything except Canon. That was my policy back in the days when I shot Nikons too.