Use LR or Aperture??

You can try iPhoto, which you should already have. It seems to use the same RAW processing engine as Aperture but with much fewer options. My own preference is to start my editing in Aperture, and then finish it with Lightroom on a second pass, where I work with TIFFs. In Lightroom I use plugins, and functionality such as keystoning/lens correction.

Both programs are very good and each has it's own strengths and weaknesses.