>>3609851The 55 is a great lens. Perfect for street and portraits. Only downside is the CA that you can get, but it's easily fixed in post. The 50/1.4 is a great lens, but you might have to go through a few because of the quality control issues. If you get a good one, then it'll be a keeper forever.
I have the 55 and love what it does for me, but as soon as Sigma announce their 50/1.2, I'm getting that ASAP
I'd also recommend the 85/1.8 if you're looking for a portrait lens. It's excellent.