Theoretically, Phage, Scream, Riot, Agony, and Lasher should all have the same strength level as Carnage, however as the symbiotes never fully bonded /and now cannot bond/ to their separate hosts in the way the Carnage symbiote has bonded to Cletus, their strength is not as refined as Big Red.
Hybrid, to me at least, feels like it should have been the strongest, as well, he was four strong symbiotes bonded to one man. This is especially exemplified when in /possible spoilers/ Deadpool vs Carnage #4, the symbiotes bond all at once to Wade, and he becomes faster, stronger, and more durable than Carnage.
Zzxz and Krobaa are debatable, they are never really shown showing a unique skill set or power.
Toxin is said to be the strongest, this should apply to Scorn too, as both Toxin and Scorn have gestated on earth, have the same parent, and fully bonded to their hosts. Scorn has the added strength of blending with machinery, so I would personally makes her exceptionally powerful.
Basically, the stronger the bond to the host, the stronger the duo is