I just registered for this site so that I could reply to your inquiry! I bought a used full frame 5D Mark I this summer and love it. (I got tired of waiting for the 5D Mark III!) After a long time looking at sample photos at pixel-peeper.com, I became convinced that prime lenses was what I wanted. Yes, changing lenses is a pain, but I love the pictures that they take. I bought a 14mm on ebay, and then with extra cash I made from my summer contract, bought a new 24mm 1.4, a 50mm 1.2, and a 135mm. Then in October, I became convinced that for the added flexibility of not changing lenses, I could live with the 16-35mm, so sold the 14mm on ebay and bought the 16-35. I was not happy with the results. I walked around my town and took photos at a 2.8 setting at 24mm with both the 16-35 and my 24mm. My 24mm blew away the 16-35, both in terms of clarity and saturation. So, having bought the lens at B&H, I sent back the 16-35 and purchased (again) the 14mm (It was on sale!). I love the 14mm because it is light (unlike the much heavier 16-35 or super heavy Nikon 14-24) and because the picture quality is excellent. So my advice: buy the 14, keep the 50, and then, when you have money, purchase the 24 1.4. My 24mm is the lens I keep on my camera most often. Oh, by the way, I did have a 24-70 a couple of years ago when I had a Canon 60D, but sold it because it was too long and heavy. Good luck on your decision!