Try a search this topic is discussed many times ( unfortunately with pretty much no conclusion )
Here is what you will pretty much get
50 1.4 - great value, great lens after 1.8 with a micro USM focus so its a bit wonky at times. Known to break easily ( I had mine for 5 years and never had an issue, others will disagree )
Sigma 50 1.4 - another great value, close to Canon L but known to has issues with focus. ( I never tried one )
Canon 50 L - Best Bokeh, useable at 1.2 but has focus shift and is very expensive.( IMO the best 50mm lens you can buy but you will be frustrated at times. I find I miss most often with this lens but when I hit its amazing. FWIW, I probably miss about 10% more with this lens then I do with any other )
Even though I love the 50L its hard to not go with the Canon 50 1.4 which in my experience seemed sharper.