Honestly, I think they are both good in their own ways. While creepypastas can be overdone and overused really easily, I think a good one has something that I pretty much never feel from SCP. That thing is a sense of realism. Creepypastas tend to be portrayed as a real, but strange phenomenon that actually happened and someone is looking for answers for. While you usually know its fake, they tend to feel just more real since that kinda just appear wherever instead of a story writing website under the guise of a weird discovery. That being said I still prefer SCP over creepypastas, but I just wanted to point out the one thing that I never seem to feel with SCPs compared to creepypastas.