The Moro arc is my favourite, by a fair margin too, though the current one has potential to top it I think.
If we're talking about just the arcs also featured in the anime, Tournament of Power is the best in comparison to the anime counterpoint. I might like the Black arc more than ToP on a base level, but I'm not sure what version I like better there. I love that the anime made Black a mystery, and had I thought, a compelling build up to the fight with him Everything outside of that mystery build-up however is done much better in the manga though, so I'm pretty mixed. I basically don't like anything about the anime's version of the ToP arc in comparison to the manga.