It is going to depend on your opponent, and also the other champs on your team. But Darius is an all around solid pick right now, and Shyv is good as well (though she lacks CC and you should consider this when choosing her teammates). Graves CAN be good... but he's slow moving and not nearly as tanky as most of the people you will be facing off against.
tl;dr It depends.
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shyvana for ranked teams
darius for normal pubstomp