If I had to pick only one it would be Revolutionary Girl Utena. Huge fan, blew my mind as a young teen. My username is actually thanks to RGU, but it's a really obscure reference.
Other favorites would include Gintama, Mawaru Penguindrum, Digimon Tamers, JoJo, Evangelion, Serial Experiments Lain, Dear Brother (the ending sucked compared to the manga though. They made it too happy). And so on. I grew up with a lot of 80s and 90s anime and manga for the most part. I really miss the old days of "intense" shoujo manga like X/1999, Angel Sanctuary, Fushigi Yugi and so on. Even back then shoujo anime adaptations typically had cheaper production or were limited to OVAs, but now it's like we don't get any at all. Would be nice if Nokemono to Hanayome got an anime.
I love One Piece too but the anime really started to burn out during Thriller Bark so I switched to reading the manga.