I like the Diet Coke logo because it's simple and elegant, yet bold. (It also doesn't hurt that I love to drink Diet Coke.)
I dislike the Pepsi logo because I think the text is too light, making it appear as if the circle is going to fall and crush the text.
This exercise paired with our mood board exercise prepared us for our first project -- creating our own logo. Stay tuned to see what I came up with.