Both phrases say the same thing, except one is positive and the other is a more negative view of it. Viewing something as "half full" is more positive because it implies that there's still something there, it's more hopeful. Vs. "half empty" has a more bleaker sound to it and a feeling attached that it's lacking half of something.
I prefer the positive version, because I try to inject as much positivity into my life and the persona I put out into the world as possible (it's my own personal preference). Words have so much affect on people listening and their interruption of your meaning. It's something I heavily try to consider before speaking. Also, "but" vs "and" have the same effect. "But" can be more negative and challenges a thought vs "and" where it's more positive and builds upon a thought.
ex.
Person 1: "The sky is blue."
Person 2 "But there's clouds too."
(In this example saying "but" put person 1 in defense of their previous statement)
Person 1: "The sky is blue"
Person 2: "And there's clouds too."
(Here "and" builds upon person 1's statement and the feel is more collaborative)