I was always a fan of FMAB but reading the source material puts into perspective how good Fullmetal Alchemist is. There's discussion about how it lacks comparable peaks to other works, but being consistently great is incredibly difficult yet Arakawa does it perfectly here. 10/10
Practically every arc is bare minimum very good but Promised Day is a standout in general, not just for FMA. Even if Challenger has overtaken it now, it's still my third favorite ending in the medium and a fantastic example of how to wrap up a story properly.
Every character in the story almost got a satisfying conclusion, and Scar in particular had one of the best. FMA was very open about confronting themes of racism and genocide, and how Scar & Ishval was handled not only throughout the story but at the end too was excellent
Another thing I appreciate about FMA is consistency in how alchemy is handled as a "power system" - not only are there many creative uses for alchemical techniques in the series, but there's a very clear and present limit to those powers and scaling is never abrupt or nonsensical
The cast overall is definitely a strong point, and even if the "female cast" is basically one character, Winry is developed really well and her role in the story never feels forced. Her interactions with Ed are always great, especially at the end of the story
Van Hohenheim is also one of my favorite supporting characters in manga, due to how well not only his backstory was written but also his interactions with his sons, and the conclusion to his character was tragic and poignant but beautiful at the same time
It's hard to separate it into my favorite arcs because of how cohesive the story is, but PD top 1 obviously
Top 10 characters:
Edward
Mustang
Alphonse
Winry
Van Hohenheim
Ling Yao
King Bradley
Scar
Father
Greed
Top 10 characters:
Edward
Mustang
Alphonse
Winry
Van Hohenheim
Ling Yao
King Bradley
Scar
Father
Greed