Till today my favorite manga is One Piece
nb: those born in the 90s surely like One Piece
one piece one of Oda Sense's masterpieces, which from my childhood until now I still read.
it has been 20 years but has never been bored with the story line.
Nothing beats One Piece I guess. We all have been following the story and Manga and now they are on the Wano Arc and it took 20 years in development. All of those past episodes including the Arc on Thriller Bark where Kaido was mentioned by Moria. Now, this is getting exciting.
I also like Hunter x Hunter a.k.a Hiatus x Hiatus. There's a rumor that by 2020 they'll be back again.