That's a toughy.
For years it used to be YuYu Hakusho — hands down. However, I've watched a helluva lot more since then, so it makes it a bit hard.
I love HunterxHunter (specifically the newer one; the older one cut it too short), which is by the same dude as YuYu. Toradora is awesome. Mushishi and Kino no Tabi are both great too. Ouran High School Host Club is fantastic for a comedy. Nana has feelz and sadness.
So, I suppose it depends on the genre? Type, etc.
YuYu Hakusho and HunterxHunter are both amazing shonen anime unlike the rest out there. Constantly making fun of what is typically shown in those types of shows and branching out from it.
For shojo, Nana is awesome. It's definitely not something people who are heavily into action or a fast-paced plot would be into, nor someone desiring a happy ending. It's a lot closer to real life than a lot of the anime I have watched. They're all adults just trying to get by in Tokyo. Sex, drug abuse, infidelity — the works.
When it comes to shows that have an overall meaning in each episode then I'm torn between Kino no Tabi and Mushishi. Animation-wise Mushishi is better, but it also came out much later than Kino no Tabi. Both have great lessons to learn. Those into the paranormal would like Mushishi more. Kino definitely keeps to realism aside from a few things, but they make it quite clear it's something expected in their world.
Ouran High School Host Club has some feels and is definitely more of a shojo, but the comedy aspect is what got me. It's goofy and lighthearted. The style is adorable and as an artist I never get tired of looking at it. The lines are really clean and the colors are nice. The ending could have been better, but meh.
Toradora is a huge feelz train. Comes up as yet another school girl harem anime at first. Where you think e'rybody is gonna be aaaaall over the main dude, but it really isn't. It's probably one of the very few anime I have seen that relatively portrays high school accurately. There are some moments that remind you it is still an anime, but they address a lot of really genuine scenarios someone could face growing up.
Wahoo! Wall of text.
