Nerd hat on!
The answers to these discussions always really depend on which version of each character, as they've all been interpreted at different power levels by different writers. (Really the answer depends on whose name is on the cover of the comic book.

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For the sake of argument, let's assume that each character is at the most commonly written level of power and that the battle would follow the logical results of that power rather than (as is usually the case) the story the writer wants to tell.
We will ignore the results of previously published DC/Marvel crossovers since those were based on such considerations as reader voting and editorial negotiations rather than examination of the evidence.
Batman vs Captain America: Their fighting skills are pretty comparable. In a spontaneous throwdown, Cap has the advantage due to the effects of the physical enhancements from the supersoldier serum. If Batman has the chance to prepare, he wins. Given enough time to prepare, Batman almost always wins.
Quicksilver vs Flash: Quicksilver can run at the speed of sound. Flash can get up to
light speed. This isn't even a contest.
Hulk vs Doomsday: Their strength is comparable, but Doomsday has super-speed, flight, and the ability to spontaneously develop new powers to counter an opponent. Super-speed is the real killer here. There's no reason that the Hulk should even be able to land a blow, given that Doomsday can move hundreds (thousands?) times faster than he can. (In general, most comics writers don't seem to understand how overwhelming a power super-speed at that level would be.)
Hawkeye vs Green Arrow: There's nothing here to really distinguish the characters besides personalities and color schemes. Coin toss.
Superman vs Sentry: Superman's powers are primarily physical. The Sentry has the ability to rewrite reality without even meaning to. In fact, there is a very good argument to be made that the Sentry is really just another manifestation of Franklin Richards' subconscious. The results of a fight really depend on the Sentry's (Framklin's?) mental state. If the Sentry is sufficiently enraged, Supes could end up torn in half or erased from history. Superman's best chance is to talk the Sentry down - his calmness, good will and sincerity might work better than punches.
Galactus vs Darkseid: I'm not sure if the full extent of their powers has ever really been established for either character. Offhand I'm going to vote for Galactus, who doesn't seem really vulnerable to any degree of physical force.
Punisher vs Red Hood: I'm not really that up on the Red Hood. Basically just a resurrected, grown up Jason Todd with guns and a bad attitude, right? I never really liked the Punisher anyway. Can we say that they both shoot each other and die?