I prefer the Corruption. Certain loots from the Crimson are better but I like the drops from Corruption shadow orbs a little better, plus the drops from the Corrupt Mimics in hardmode. Corruption chasms are more challenging than the Crimson chasms, and I actually found the mobs and boss a little harder in the Corruption than Crimson. Lots of Corruption enemies go through walls, like Clingers, Devourers, World Feeders, etc and they always take me by surprise, but Ichor Stickers, Herplings, etc from Crimson get stuck in narrow spots since they can't move through walls. If I remember right, only Crimson's Floaty Gross goes through walls but they can be easily seen unlike Corruption worms and Clingers. (them darn Clingers always pop out of walls, and shoot me with fireballs) Ichor Stickers I can spot more easily and I find the streams of ichor a bit easier to get away from than the Clinger's fireballs, which shoot further. I also think the Scourge of the Corruptor is my favorite weapon. It's excellent for crowd control and has saved me from being swarmed by mobs and a Paladin on many occasions, and in the same situation, I almost died using Vampire Knives, as they couldn't heal me fast enough against the mobs and couldn't kill them fast enough. The Scourge is much stronger, but the Knives are still great against bosses especially with the proper setup to heal even more. That said, I prefer the challenge of the Corruption more, plus the Scourge of the Corruptor against large mobs and certain bosses, but I still enjoy the Crimson and the Vampire Knives for boss situations and smaller mobs.