I know a lot of people always recommend the 50 1.8 as a lens you have to have, but for portraits I do not think it is the best option, even considering its low price. It can be very sharp, but for portraits, very sharp is not that ideal. Certainly not the first thing I look for in a portrait lens.
More important to me is how the lens renders the in focus areas as well as out of focus areas, and also the transition between the two. I think the 50 1.8 has characters that make it very good for product/item shots, but not the most suitable for portraits. Further, the focal length of 50mm can be effective for portraits, but is not ideal and can get very confining if that’s all you’ve got (too close for head and shoulders, too far for waist up/full body).
Personally, my current favorite recommendation for a relatively low cost portrait lens would be a used Nikon 35-70 2.8D. I prefer it over my 70-200vr for portraits, but use both depending on the focal length needed.
-Suntan