Every guy has his own preference as to how to place his dick in his UW to feel comfortable. When I used to wear briefs (don't anymore) and when I wear cycling shorts, I lift my dick and balls straight up out of the way of the crotch. Have to keep the goods away from the bicycle seat.
Gravity comes into play, and unless you wear horribly tight underwear, your dick won't stay up. I hate when it hangs in something tight, so I've been wearing boxers for the last 4 years or so. If it's going to hang, give it room. My dick curves to the left. As long as it works and gets the job done, I don't care which way it curves.
I think that anyone worried about the curve in his dick should wear boxers or freeball and see if it straightens over time. Loose feels better to me than snug.