50mm or 35mm lens for a DSLR with 1.6 crop factor?

I have a Canon 500D, with the original lens EF-S 18-55mm f/3.5-5.6 IS II. I would like to try a prime lens, but I don't know whether I should choose a 35mm or 50mm lens.

I read that the 50mm was great even for portrait, so I'd like to try it. However, as the crop factor of the 500D is 1.6, does that mean that I should by the 35mm ? (35 * 1.6 = 55).

I may have missed something, and perhaps my question makes no sense. I apologize in that happens to be the case. Either way, I'll learn something.