I can't say too much about the sigma's since I have no personal experience with them, but I just got my 50mm 1.2L in a few days ago (coming from a 50mm 1. and I'm incredibly happy with it. Probably won't come off my camera for a while!
I think the 50mm 1.
is the coolest lens on this forum. I've done it so many times without noticing (hint: smiley)!
EOS 5DIII, EOS 5D | Rokinon 14mm f/2.8, TS-E 17mm f/4L, EF 24-70mm f/2.8L II USM, EF 35mm f/1.4L USM, EF 100mm f/2.8 Macro USM, EF 135mm f/2L USM, EF 70-200 f/2.8L IS II USM, 1.4x III, 2x III | 600-EX-RT x3 | EOS M + EF-M 22mm f/2