First off the battle would be with literally EVERYONE from the marvel and dc universe, including villains (The villains would be helping the heroes, ie Joker would be helping Batman to defeat Spiderman)
I believe Marvel would win and if you disagree post your argument and I believe I can counter act it.
Judging from what I"m reading I believe you mean which characters would win rather than which is a better comic company and how well each company is doing. Therefore I will begin with the best comparison, the Avengers in the 2012 film and the original JLA
First of all, Batman would defeat Iron Man. He would use his EMP rifle that we saw in the Dark Knight Rises to turn off the electronics of Iron Man"s suit rendering it useless in battle and Tony Stark just a regular guy.
Martian Man Hunter would defeat Captain America hands down. Captain America has nothing but his shield to defeat a shape-shifting, energy projecting, invisible, super strong, telepathic alien. Get the point. Captain America does not stand a chance.
Superman, being super fast, and having superior weaponry would defeat Thor. The only chance Thor would have would be to find Kryptonite, but Superman also has an Anti Kryptonite suit to negate this effect.
Black Widow is just a trained government agent who definitely couldn"t beat hawk girl who has actual powers.
Wonder Woman would defeat Hawkeye by deflecting his arrows with her indestructible wrist bands and then beat him.
Finally Hulk, the only Marvel avenger who poses much of a challenge Could be flown into space by Green Lantern as Green lantern does to Grundy in the video game Injustice.
This gives a comprehensive look at some of the main superheroes from each which clearly shows how much stronger DC heroes are than Marvel Heroes
First off, I said Marvel and DC Universe, not Avengers vs JLA. Secondly you are taking two random characters and making them fight when it is an all out battle, you used the example, martian manhunter vs captain america= cap loses (Which I (sadly) agree with) However, Martian Manhunter and Cap might never even meet each other in battle, who`s to say Hulk doesn't get to Martian Manhunter first? Then Martian Manhunter is screwed. See what im getting at? You also have to think of smaller characters, not just the mainstream ones. And the villains too! If almost any of the DC hero's go into space, they would be completely obliterated by Galactus, no doubt about it! The dude eats planets for god's sake. Also, Green Lantern (As awesome as he is) would not be able to take down Hulk, Yes I played Injustice he did take Soloman Grundy into space, but Hulk is without a doubt way stronger than Grundy. Black widow (as you mentioned) would be on the ground fighting, while Hawkgirl would be flying around fighting probably Iron man, Thor or other characters who can fly, same with Superman. Iron man would not be defeated by Batman as iron man would already know of his EMP rifle and tell another hero to take care of him. Most peoples arguments are simply, Superman. Well, 5 characters could take down superman (especially when they're working together AND they have the help of any other character in the Marvel universe) Iron man, Thor, Hulk, Galactus and Deadpool. Deadpool could easily be a distraction to Superman and would be able to avoid/cope with all his attacks. Iron man is very rich and powerful, he would definitely be able to get his hands on kyptonite and make a kryptonite weapon or even a kryptonite suit. Remember, Iron man is much more powerful than the last few live action movies. Thor would also be able to keep Superman fighting or draw him places. Using Mjonlir to break his jaw and keep him fighting and keep coming back for more. Hulk would put up a big fight against Superman and end up getting so angry he could simply pin him down without him being able to even move(Remember the angrier Hulk gets the stronger him and his powers get). Once they get him in space, Galactus would EASILY grab Superman between his fingers and literally turn him into dust. Poof, Superman's gone. Your move... Remember the villains. (Jeez I just helped you a ton with your argument there are plenty of insanely strong DC villains)
To begin, I understand that you said Marvel and DC Universe, however it is such a broad topic that I chose to use Avengers vs JLA as a starting point to show you that DC characters are comparatively better than marvel characters. If we were to make an argument for every DC and Marvel character in the Multiverses then we would be here typing out arguments forever That is why to simplify things, I began with Avengers Vs JLA.
Now one of your main arguments is that Superman would easily be defeated by a tag team of marvel characters, however, if the five characters you mentioned are working together, then why couldn"t superman be working together with superboy and supergirl, the three of them together would easily be able to take down iron man, thor, hulk, and deadpool. And as for Galactus, your apparent trump card who can obliterate any DC character in space, Krona with his immortality, and ability to absorb any energy into his body, including his foes, he could easily defeat Galactus. In fact he did defeat Galactus during the JLA/Avengers miniseries.
And in case you are looking for more, the marvel univere is severely outnumbered when you factor in the 7200+ members of the green lantern corps and however many members are a part of the Sinestro Corps. Overall, not only is the Marvel Universe outnumbered, but it is also out powered.
Extend all previous arguments.