First, asking this on a Naruto forum, the answer should be obvious what people choose.
Second, most people here are biased and don't realize what the word Greatest means.
Third, everyone is just going to pick what their favorite anime is and call it fact without no proof to back up what it is so great.
With that said, the greatest is Astro Boy. Without Astro Boy becoming popular. It never would have encouraged mangaka's to start writing making manga and anime what it is today. DB would never have existed, nor Naruto.
Now from you list, it is either DBZ, One Piece, or Pokemon. All three of these have done so much.
Even though DBZ is horrible in all aspect of what makes a anime/manga good(beside fights) it was a gateway drug, sort to speak, to getting people to view other animes. I wouldn't even put it in my top 10 list but there is no denying what it has done.
One Piece is the most popular anime to date. It has sold more volumes world wide, and has passed DB is total sales. That by itself should say a lot.
Pokemon is by far the most known anime. You show grown ups Pikachu and they know who it is. You show them Luffy, Goku, or Naruto, and they have no clue who they are.
Best short anime imo is either Code Geass or Full Metal Alchemist: Brotherhood. The problem with comparing short animes to epics like the big three DBZ or Pokemon, they didn't have the time to get popular because they haven't been running that long. There are so many good short animes and mangas out there that surpass the long running ones in everything, they just don't get as popular because of how short they are. This makes comparing short animes with the longer running ones hard.
I'll just leave it at that. Getting too long.