As both are clearly douche bags I would definitely go with Sharon. Piloting the SDF-1 whilst piloting a Ghost so superbly TWO fighters could barely compete before one went all suicidal redemption on it was impressive.
On the rape, I think it's left intentionally vague as well. He certainly did SOMETHING, likely more than we saw, but how far along and how horrible it got is just better left unsaid, that's a dramatic device. Macross has a lot of "open to interpretation" moments. What I don't get is where anyone could find Isamu "likeable." I think he could have been made likeable if the series was longer but I didn't see it in what we got. A punk who pretty much always gets what he wants whereas Guld is the person who constantly wants more than he has (or, more specifically, what Isamu has).