First lets go over what your profile picture should be set up like according to Facebook.
Facebook offers these instructions for creating your profile pic:
Page profile pictures are square and display at 160×160 pixels on your Page. The photo you upload must be at least 180×180 pixels. We recommend uploading a square image. Rectangular images will be cropped to fit a square. Your Page’s profile picture will also display next to your Page’s name around Facebook to represent your Page.
So basically, Facebook’s image dimensions say your profile picture should be: square, at least 180 pixels wide & 180 pixels tall, not a rectangle (or it will get cropped)
Ok so let's talk about what kind of picture you should use. In the world of Social Media, with emphasis on social, we forget that our first view from another profile is our very own profile picture.