Mac coming, what is the best photo app?

So I have a MacBook Air coming in the mail and I already did a post over in Applecore about the best text editor as I am a writer but I have gotten into photography a bit lately and though I really like VSCO cam on my iPhone 5, I have been thinking about investing in a high mp shooter and getting a good photo app for the Mac. Anything that stands out that is a must have for a novice photo editor looking to improve his skills? Thanks.