Best image viewer for OSX?

Here's the deal -

24 hours ago I got my first Mac, a rMBP and I'm loving it so far and have been finding alternates to what I've been used to on Windows.

The one thing I can not stand is trying to use iPhoto and/or Preview to look through folders full of images. I'm looking for something like the Picasa Image Viewer (not their photo editing/organisation tool) on Windows, which is by far the best viewer I've ever used. It's fast and extremely intuitive. Open any image in a folder, it scales it to fill your screen, and you can use the arrow keys to quickly fly through every other image in that folder - no need to select all images before opening them.

I've tried Xee and Sequential, and Picasa for Mac doesn't seem to have an image viewer. I don't need any editing tools, I just want to look at photos quickly without having to manually resize the window, zoom to fit or click a button to skip to the next photo.

Apple Core - I need your help! What's the fastest, simplest and most intuitive image viewer for the Mac?