RegExr looks really nice, but my go to is still http://rubular.com .
What do you think makes it better? I think the UX on rubular is much cleaner. Don't they both serve a different flavor of regex?
Having the numbered capture groups and clean simple interface is amazing. I also test and create tiny urls embedded in my code to show how the expression work. Handy for coming back later and making changes.
I don't doubt there is something better, but it is still hard to change.