Depends on the series. Phantom Blood is pretty meh, Battle Tendency is far and away the best one that's been animated so far, Stardust Crusaders is really strong but it does drag in quite a few places, and Diamond is Unbreakable starts strong but really starts petering out about halfway through.

You'll have to be down with Araki's ultra-butch designs, but they grow on you. It can get pretty violent, but never so over the top it's grotesque.

So basically: I recommend Battle Tendency and Stardust Crusaders. Battle Tendency if you want something a little more goofy, Stardust Crusaders if you want a little more lore and seriousness.