A bad blend vs a good blend depends on what you want really and the sound/feel you need.. the only "bad" blends to me are overly buffered ones that give you volume issues like barge and boss.
I think my all time faves are the Katanasound super bass fuzz [duh], the Fuzz Hugger Bassbloom and the MASSF Stary wisdom... that said I find that lately having a bunch of pedals with blend don't work for me as much as using a blending looper and putting a bunch of pedals in there [some with their own blends] to achieve the sound I want.. and so know I'm having a custom 5 loop looper that is a 3 and a 2 in one box so I can have the first 3 loops blend and not the last 2.. life in complex and stuff.