My favorite anime is Hellsing: Ultimate. It's an OVA that covers every volume of the manga, each volume is one episode. The classic anime is pretty much just filler arc (and very bad).
Hunter x Hunter is not entirely good--some of the seasons are obnoxious and, therefore, difficult to watch--, but it has the best arc of all time: the chimera ant arc.
Shingeki no Kyojin, AKA Attack on Titan, is a modern classic and a must-watch. Twenty years from now, we will remember SnK as we remember Cowboy Bebop and Evangelion today. The new season has 3D Titans though. It's a little ugly, but still worth the watch.
FMA: Brotherhood, Parasite, Devilman Crybaby, Interspecies Reviewers, Gantz... They are also some of my favorites--the ones that I remember off the top of my head right know. Asked yesterday, I may would have come up with a different list...
One Piece is my second favorite manga (behind Berserk), but the anime has a lot of filler arcs and the sound design is hideous, so I prefer the manga.
For the ones that did not get anime adaptations yet, I have a lot of hope for Chainsaw Man and Spy x Family.