Yu Yu Hakusho
When I was a kid, I watched this, DBZ, and Sailor Moon on Toonami after school. I never finished YYH back then. So over a year ago I decided to watch it from the beginning on Hulu. I took a break at some point in the middle of the Dark Tournament arc and just picked it up again recently after I finished watching FMA 2003. It looks like I actually watched the Chapter Black arc as a kid, but not the Three Kings arc. Now I'm finally done.
Having now watched the whole thing as an adult, I'm impressed at how cool the show still is. It really stands out compared to other kids shows.
I don't have a ranking for the arcs yet, but I liked all of them.
Now that I finished that rewatch, I might do Log Horizon S2. I recently rewatched S1 and stopped there because I didn't like S2 as much, but now that S3 has been announced, I might as well. Still holding off on watching FMA:B. Need some more time to pass from having watched FMA 2003. Might go for something drastically different. I haven't seen stuff like Your Lie in April and March Comes in Like a Lion.