Both are highly capable apps, and have their supporters - there's no wrong choice between the two.
I wound up going with Aperture when the App Store came about, and with it, that dramatic price reduction. At that point, and knowing I tend to get on with Apple's UIs, I went for it, and have enjoyed all the flexibility in post-processing that it's brought since.
The catch, as it were, is that (for now?) the App Store doesn't support any upgrade pricing - as and when v4 comes out, it'll be a completely separate purchase. But, at that sort of price point, it still works out advantageously, and without any need to confer with the vendor regarding license verification.
I do wish Aperture 3 offered lens correction, although I've yet to encounter any such that really works particularly well with chromatic aberration correction on the Tamron 28-300mm f/3.5-6.3, which I used for my initial work - not a terrible lens, but certainly prone to CA at the long end, not helped by my subjects often displaying white tails against dark backgrounds.