By far a Mac, I bought myself an iMac and I just have to say i've been blown away with it so far, it's great for graphics, editing, and everyday web use.
I find myself often times editing videos and making art for my channel, i've never been more impressed with a computer before.
Before I bought my mac, I found my windows computers running into issues quite often, and with my mac I've never had a single issue.
Not to mention the wonderful display, I don't even have retina and it's just awesome.
I could go on for days but I figure you most likely already have made your decision. Anyways, let me know if you get a mac, I can help you with anything you might need help with on OS X.