I got a Sigma 50mm f1.4 lens from a fellow POTNer and I absolutely love it. I love it so much I would like to keep it on my 5DII at all times.
But you know what...it just doesn't make a good walk around lens. It's not wide enough or provide enough reach. It's simple as that. 28-75mm Tammy provides more versatility and I'm sure 24-105 isn't too bad (used to own it).
For portrait work, sure I'll slap on the 50mm or 85mm. But not while running around outdoors.



