It probably depends on the writer and circumstances.
Venom is stronger, faster, and far more resistant to physical damage. On the other hand, Sabretooth is more skilled and ruthless.
Venom has a weakness to fire that even Sabretooth could take advantage of, but on the other hand Sabretooth has tiny claws that should have a hard time piercing through the full-sized Symbiote.
Does Sabretooth still have an adamantium skeleton? If not, Venom should probably have the advantage.