For portraits you tend to want a slight telephoto to compress facial features (nobody is happy with their nose). Typically you want 85-135mm (or more).

While the 50mm "acts" like an 80mm on your crop body, that's only in terms of framing. In terms of compression it's still a 50mm. We love our 85mm f/1.8 for portraits, and people like it for indoor sports, but it's a bit long for indoor general purpose. If you're solely doing portraits, I'd recommend it over the 35 or 50. If you're hoping for multiple uses out of the lens, you'll have to figure out what those uses are and which are most important.