i will state now i am an aperture user
i have played with both, been using aperture as my main photo software since version 1.0, tried every Lightroom beta that has been out as well, so can only comment on the beta versions. I purchased aperture as a boxed software when it first came out, so the current price is a bargain, and is something that Lightroom still cant match. Another thing to consider, if you have multiple macs, then the aperture purchased through the store can be installed on any using your apple id.
I find aperture a very simple way to manage everything, just leave it to do its work and it will look after all your files, contained in one easy to backup location. Lightroom on the other hand uses the file system you have stored on your computer.
Personally i prefer apertures approach to it all, i do keep trying out Lightroom every now and then to see how it is getting on and whether to switch, ultimately i am very invested in apples way of working and find it hard to transition back out of that, i like the simplicity of not having to worry about my file structure. I also find it easier to organise my photos in aperture.
I did find Lightroom to be simpler to achieve certain results when editing a recent batch of photos though, but still found myself resorting back to aperture with the exported edits, the edits were achievable, it was just quicker in Lightroom to find the particular adjustments. However i do not like lightrooms having to switch between library/develop to edit photos, aperture is much simpler for doing quick edits.
Its no secret aperture is a resource hog on your system, so depending on your machine that may be a consideration too. Cant comment on how lightroom performs though.
But from my perspective there is nothing in lightroom that is prompting me to change from aperture, books and gps intergration have been there for a couple of years now, and both are very simple to use in aperture.
For a new mac user looking for new software for photos, you cant go wrong with aperture at its current price point.