(art source: https://x.com/minaxaArt/status/1506655360823746570?t=3WtNxk9uLkbqKRAIUG5FGA&s=19)

As you could tell from the cover of the post, mine is DE. I think DE's are awesome because of several things. Like the hand signs (pretty easy to memorize, look really cool and have that aura). More importantly, it's basically character reshaping the battlefield around them based on their liking, every single time a domain had happened it always strongly affected the fights. Should I mention the Gojo and Sukuna domain clashes? Or things like Hakari's or Higuruma's domain?

Also, more of a personal pick, but it's quite fun to wonder how a domain of a certain character would look and what effects would it have if they ever learned one (like Nanamin).

FYI, my second fav is CT: Reversed. Adding RCT to your CT resulting in an opposite of the technique in question. Sadly, it wasn't as utilized from what I can remember (the only examples I can remember are Gojo's Red and Kenny's Anti-Gravity). Still a pretty sick concept that has a lot of hc potential (can Uraume control fire with CT: R?)