The Creeper is dangerous but when you're wearing armour it's suicide blast isn't that bad and I actually end up employing them to clear hills in the way of progress.
The real danger is Spiders. This is from the perspective of someone who now plays exclusively on a survival multi-player server. Latency issues betray how fast Spider's actually move, and unlike zombies there is no delay between there attacks.
If a Spider is standing remotely near you, it will hit you again and again and again, dozens of times in about three seconds. Armour gets whittled and you get thrown everywhere.
Between aggregating damage and flying off cliffs, Spiders cause the most anguish after dark, in my experiences.