I'm using both Aperture and Lightroom, but, have not been doing so for very long... Used to shoot jpg straight up and faff about in PaintShopPro.. If I had to choose only one to use going forward, i'd have to choose Aperture right now as it just seems a little more streamlined and thought out - things feel like they are where they are meant to be, does that make any sense? Love the way stacks work in Aperture, importing is a piece of cake, workflow is great.. all very simple, but has everything I need (for now) if anyone is interested, I posted a question to a group over on FlickR
HERE, asking what people used to upload to flickr.. lots of Aperture / Lightroom etc... makes for an interesting sort of tally.. only if you're interested.