I've only purchased pedals this year, so:
Worst: NuX Sculpture Compressor, It was OK while it worked, if a bit mild, but has stopped working. Which might be my fault, since I connected the wrong voltage to the PSU that was powering my pedals and popped a cap in that. I'm not certain of the timing, though, and it's still responding to the switch - just no output.
Best : IK Multimedia Tonex One. Despite the software being horrid, and a (fixed) problem I had with its license just vanishing from the IK Product Manager, it's worth it because using The Fridge really feels like playing through an Ampeg SVT. It does that thing that makes me sound more professional than I am.