Venom is stronger and more durable then Spider-Man, but I would give Spidey the speed and agility advantage. I think Venom would win more often then not against Spider-Man, but to say that Spider-Man could not affect Venom at all with his punches is ridicolous - these two have had fights that have lasted for entire ISSUES, and Venom isn't excatly laughing at Spider-Man's punches in them.
With all the skills here, he might be able to affect him on stuff like pressure points and such, but with the symbiote, that is doubtful. I'd still give majority to Venom.
Spider-Man on his lonesome isn't capable of defeating Venom in the long run. He would certainly be able to hold his own for hours, but he doesn't have the necessary strength to bring him down for good. And Venom would certainly feel his punches.
The venom symbiote, after bonding with Spiderman, kept the qualities that Spiderman had. Eddie Brock, who had olympic-level strength BEFORE the symbiote, had his strength accelerated far beyond what Parker did. Venom then absorbed a second symbiote, and his abilities shot into the Class 70's.