1. I am not really sure which company is "more successful." DC has been in print longer than Marvel. However, Marvel may be financially worth more right now. Marvel may have more of the print market right now too. That being said, I don't really care who is more successful. I wish that they are both successful because that is just more for me to enjoy.
2. As far as the success of storytelling, that is subjective. I like both, but I understand if people like one over the other.
3. As for who has the more powerful characters...i
t doesn't matter. If we continue down this route, the argument gets really stupid. We'll end up at Death, but both companies have their versions of Death. So, which Death is more powerful? Or, Marvel even met God, who was in the form of Jack Kirby. DC has God and Jesus, too. Now it becomes some comic book religious debate. DC's God and Jesus vs. Jack Kirby. We might as well sit here and argue Christianity vs. Buddhism.
Are you talking sheer power or are you talking about stories/characters/development? Marvel is way more successful than DC these days.
If you're talking Cosmic beings Marvel has a lot of very powerful ones like Galactus, Thanos, Apocalypse, Silver Surfer, Beyonder, Captain Marvel, Death...to name a few. There are more but they're not as well known as the DC ones.
DC has only a handful of characters I actually like or care about, Marvel has way more. However Batman will probably be one of my fav all time characters.