As in all comic book debates, everything really is too close to call.
Bats v. Cap...obviously Bats...cause he's the Batman. But Captain America is no slouch, and I don't think that Cap would just roll over, I just think that Batman would eventually have some sort of Anti - Captain America Spray somewhere on his utility belt that would give him the edge.
Superman v. Hulk...Superman lost to Doomsday once, not all the time, but all it takes is one good shot. Hulk doesn't know when to stop, I can see Big Green taking down Big Blue after a long drawn out battle that would destroy any city that held it.
Iron Man v. Green Lantern...Depending on the Green Lantern, it can go either way, Hal Jordan I think could beat Tony, but not Guy Gardiner. John Stewart would give a tough fight, but not Kyle Rayner. Even deeper into the Corps, I think Tony would be able to pull off victories over most of them. So splitting this one.
WW v. Captain Marvel...I would give this to Wonder Woman mostly because she has been around longer, and has the amazonion background to give her the edge.
Canary v. Widow...Not a clue, although I think it would be a better fight than Mayweather/Pacquiao.
Green Arrow v. Hawkeye...Personal reasons I'd give this to Arrow. He's always been my favourite, and nothing against Hawkeye, I just don't see him losing. Especially if Batman wins his round.
Flash v. Quicksilver...The Flash has more experience fighting other speedsters, I think he'd be able to keep Quicksilver on his heels long enough to beat him.
Vision v. Cyborg...I like Vic, I really do. But Vision was created by Tony Stark, and I think, like Tony, he always seems to have a trick up his sleeve (in his circuits?). Plus he stopped Ultron.
Scarlet Witch v. Martian Manhunter...meh...I'm not a fan of either character, and it will take a lot to convince me otherwise, but if I did have to pick a winner, I would not put it past Wanda to set fire to a few things to gain the upper hand.
Thor v. Aquaman...What happens when electricity hit water? Fried fish anyone?!?
I don't see a clear cut winner, except for Thor frying the Sea King, but other people will have different thought than I do. And it may be a clear cut winner for either side with their views. But that's what is great about comicbooks and their cinematic counterparts, the fans will always be interested, and will always be willing to watch, discuss and criticize.