Best for what? That's not really a valid question. And what kind of option is 'dumbbell'? Do you mean DB Presses of some sort? And why are the Flies and Dips possessive? Do those options mean using the exercises of flies (insects) and dips (morons)?
OK, I'm taking off my Grammar Nazi boots...
If it helps you any, I like using Flies as a finishing exercise. I find that it really destroys my pecs if a I finish off with a dropset of flies. It's really brutal stuff.