If it is just a random encounter then I think Spiderman takes out Batman. If there was one street or sort of near street level character to take out Batman it would be Spiderman.
His power set should give Bats all sorts of trouble. I love Batman don't get me wrong but the combination of Spiderman's strength, agility, durability, web shooters, and spider sense win this fight for him though it would still be tough.
But where Batman is fast, Spidey is faster. Spiderman's strength combined with his agility and Spider sense and web shooters allow him to dodge or shrug off a lot of what Batman can dish out. All the batarangs and gadgets can't do much if your opponent can evade them all.
All Spiderman has to do is tag Batman a couple of times and he would win.
Even though I'm not really a fan of Batman and I loved the Spiderman comics as a kid, I gotta go with Batman. The dude probably has some super-high-tech-situational-anti-spider-gadget in his utility belt for such an occasion.
They would likely never encounter each other anyway since they're both from different universes. Unless Marvel and DC decide to do another crossover, and have Peter Parker and Bruce Wayne fighting for some reason.
Hmm... i have adore Spiderman since i wa sa kid but so did i adored Batman.
Both of them are the flag ship of their companies and boh of them are genious, though Bruce Wayne has something Peter Parker never had: money.
Guess no one would win, they realize hey are both good guys and ended up makin an alliance like they did in that crossover against the Joker and Carnage.