If it were published,, venom defaintly wins because of fan appeal. However, if we are talking literal than venom and most other of villians and heros have little to no chance, as long as it is a master predator hunter. a master predator hunter can take on an entire brood of aliens alone, Not even superman can take on an entire brood of aliens without angst., and fatigue.
The predator has too many spectres of vision for Venom to get away easy. He would find him in no time and Venom wouldn't expect it.
I presume that wouldn't be a first time for the Predator to encounter a symbiote, or something like it.
Venom is not resistant to fire right? well that laser cannon that the Predator packs is really hot and burnin. If he shoots him with it Venom is gonna have real bad indigestion.
WHAT would venom be able to do? Really? First of all, when the pred's cloaked, venom can't see him (for the most part). Secondly, the pred has his plasma caster (shoulder canon) which would pretty much kill the symbiote, even at low power. Venom cant use his fumes to knock him out, as his mask provides him with his air, and i'd be willing to be the pred has its own tactics for dealing with symbiotes of all sorts....
My vote goes to Venom, just because he's faster and stronger and has some kind of spider-sense. All the weapons in the world don't help if you can't hit your opponent. Venom is not a sitting duck.
I don't say Venom will have it easy, but in the end, Venom will tear the Predator apart and eat his brains.