Why is the Sigma not popular, or better yet, why do you like it?
Well, always people blame lens they don't ever use ! I've heard some complaints about the slow AF. I admit that some times the AF needs a very contrasty area to work. And most of complainers point out the vignetting ( which can be easily sorted out with a good software).
I actually bought this lens to take pictures of a wedding of my GF daughter as I didn't want to change prime lenses every 5 minutes.(it was an official photographer to cover it), so just for my pleasure. (I didn't take any pics in the church as I didn't want to bother him).
So, I planned to resale it after the event, but I found it so convenient (and optically good) that I am not sure I will resale it !
It's perfect fot travel.