"U" Logo Concepts

Working on a new logo for my personal project, Undernet. Having a hard time choosing a concept, but I'm loving all of these ideas. Input would be awesome!

Check it out the project (and existing logo) here:
https://www.undernet.io

Undernet is a front-end framework providing CSS and JavaScript components. It started as an exercise in learning better standards in CSS and UI development/design but has since evolved into a functioning library. It's still very young but I continue to work on it as my passion to generally improve the front-end developer experience (and of course, to continue learning).