Its still a bit premature to add a guy like Bannister. Adding him is fairly similar to the Manny Para hype, after one good outing there were over 4000 adds on Para and then has a rough second outing and is immediately dropped. Now I'm not saying Bannister is going to struggle, if you have a guy on your team you would really like to drop its not too far fetched to stash Brian on your bench and proceed with caution in playing him.
I do like Greinke however, hes a guy I have added in a couple leagues and hes fairly proven and has the stuff to continue his hotness.
Tomko really should not even be considered, his brutal track record speaks for itself.
If Soria is remotely available in your league ADD HIM!! Solid closer and provides some nice Ks too add to his saves, not to mention the Royals are winning, go figure
I suppose if your league is really deep you could go ahead and add some of their bullpen but in all seriousness unless your league counts holds relievers are rather useless.
Royals have some solid young arms, definitely pay close attention, but yes they have started off better than expected.