The Sigma 135mm F1.8 DG HSM Art is very sharp, focuses quickly, is built tough, and gathers a heck of a lot of light at f/1.8-which, combined with the long focal length, nets shots with extremely blurred backgrounds.
Razor sharp; Wide aperture; No distortion; Minimal falloff; Dust- and splash-proof design; Focus limiter switch; Available for Canon, Nikon, and Sigma systems
Quite heavy; Expensive; Omits optical stabilization; May require focus adjustment