First of all, this OP is weird and vague. Sonic is 5-A but which one when there are three 5-A keys on his profile? As such, it seems people are drawing from the abilities and or stats of all three keys and just giving them to Sonic for free while Mega Man just sits there. If that's not the case, then it's still confusing overall for the debate since we don't know which Sonic is used here specifically and mix ups are bound to happen. Doesn't seem very fair. It seems like whoever made this made several other Sonic versus threads (some of which were stomps) for the chance to give him wins- oh wait. But I digress.
Also, I just wanna say a few things. I don't understand how Sonic being an expert at CQC is one of the bigger factors when he's literally fighting an expert on projectile combat. An expert CQC versus an expert marksman? Seems like they cancel out if you ask me, which then brings their other abilities into question.
Ring Time? Seriously? The ability that turns fodder enemies into rings? That's kinda like saying Mario can just one-shot anyone by stomping on their head cause he does so to fodder Goombas and Koopas. If you're going to use that, then Mega Man can use an M Tank when his health is full to just make Sonic into a 1-UP. See how ridiculous that sounds? Especially when Sonic is fighting an enemy who's slightly stronger than him in this case. That's just an insult.
Sonic having mid regen and resistance to being frozen and generic ice are easily stumped by Mega Man's nigh-AZ to AZ weapons. Sonic has no resistance to that whatsoever.
Sonic has more experience because he fought a character who had more experience than him? Is this an RPG game or something? So, you're telling me Sonic gains Emerl's thousands of years experience from beating him? If that's what's being implied then that's not how it works. Me beating up a WWII veteran or just a Marine in general doesn't mean I gain the experience and training they've gained or something.
Also, PSA to everyone who doesn't understand Centaur Flash. It's a weapon that stops time for a
split second to warp space and damage everyone in Mega Man's vicinity while bypassing conventional defenses like shields and armor. It's a space-time weapon generally speaking. So no, it's not like Time Stopper (which is just time stop) or Flash Stopper (which isn't time-related at all). If
anyone delved deeper into the mechanics of the weapon as opposed to just glancing at the summary on the wiki page or Mega Man's crappy outdated profile and trying to make someone else look like a fool, then there wouldn't be a problem. Also, Centaur Flash stops time for a
split second for everything, so Mega Man, as well as everything else, not being able to move for a split second isn't detrimental to Mega Man more so than it is anyone else.
What is this argument that "Sonic has fought robots his entire life?" What is that? As if comparing the wacky fodder robots to Mega Man is a just comparison. That's in addition to Sonic also being "used" to weapons like Mega Man's. The same could be said for Mega Man and how he resists black holes, petrification, elemental weapons, hacking and several other natural resistances due to being a robot and not a biological being. Both cancel each other out pretty well here albeit they have small advantages here and there with certain abilities. Mega Man has never fought someone like Sonic? Well, Sonic has never fought someone just like Mega Man. The things being argued for Sonic can also be argued for Mega Man as well.
Mega Man and Sonic both have similar tactics. They both adapt to their opponents fighting styles and they're both intelligent overall in combat. But obviously, I'll vouch for Mega Man. Mega Man adapts to his opponent's fighting styles quickly and, based on their combat style or weaknesses, he's very resourceful in that he uses just the right weapon to put his enemies down fast. For example, Tengu Man's flight was stopped when Mega Man froze his feet to the ground. Quick Man's speed was trumped when Mega Man decided to stop time and use his speed against him. Pharaoh Man's emergency systems were taken advantage of when Mega Man used Flash Stopper to emit a light powerful enough to active said emergency systems and cause Pharaoh Man to freeze in place and leave him vulnerable to attack. This is what Mega Man does (which is apparent from ALL of his games) and it's apparent he's very good at finding weaknesses. Hell, Mega Man was even smart enough to predict where Flash Man would appear
after a
time stop and destroyed him by shooting at the predicted spot where he would appear (this is how Mega Man works his way around time stop and Mega Man has fought under the effects of being slowed down in time too). Mega Man is so intelligent and lethal in combat that he defeats new and powerful enemies designed to be powerful than him in all aspects on usually his
first attempts. This lead to him defeating foes like
Sunstar even
without any weaknesses. This is what Sonic is up against and I've yet to see what he can do against this.
And Double Gear System anyone? Mega Man literally quadruples his overall speed (combat speed, running speed, reactions, etc.) and can use it as many times as he wants (granted he doesn't activate his cool down). Also, his overall AP is boosted as well possibly to the same degree as Speed Gear (probably).
So I vote Mega Man due to high versality to get him out of a lot of sticky situations, superior range, significant stat boosts to his AP and speed, arguably better combat intelligence, AZ, his own resistances to Sonic's arsenal as well as other miscellaneous weapons like attack reflection, corrosion/acid, AoE/screen-nuke attacks, weather manipulation and some small other weapons that could prove useful.