I want to buy a phone like an Apple iPhone 6 or a Samsung Galaxy S6 Edge. Which one would be better in the sense of: having a great battery life, seamless performance, great camera quality, and robustness?

They are both excellent phones, so it really comes down to which ecosystem you prefer: Apple's iOS and the Apple Store + iTunes, or Android and Google Play. When doing your comparison, keep in mind that the iPhone 6S is about to be launched and