Daily Life Arc
Arcobaleno Trials Arc (Anime Only?)
Inheritance Succession Arc (Anime Only?)
Future Final Battle Arc
Inheritance Ceremony Arc
The Curse of the Rainbow Arc
? (Current Arc)
Hmmmm. Im going with the Varia arc
I quite liked the Future Arc.
The Varia arc is my favourite; I think the manga peaked at that point.
Future Arc. Love seeing the part where Tsuna see the former heads of the Vongola and especially the Primo. The Varia Arc is a close second though.