I'm wanting to say Ed Elric; he's pretty kick ass. I mean he beat some of the homunculus and they are practically immortal. If he can kill an immortal being he can beat anyone. Plus his ability to make shields and weapons is a big advantage.
I'd have to say Homura Akemi from Puella Magi Madoka Magica would do a pretty good job at winning an ultimate battle. Please note that this answer will include spoilers about Homura's character. :) 1. Undying dedication- Homura's strong sense of justice stems from her need to repay her friend Madoka who dies for her sake, and Homura is willing to repeat the same bulan over endlessly in an effort to savesaid friend. She feels dedicated to Madoka and holds her precious for simply being nice to her while she was alive, and for that reason Homura decides to repeat time until she can find her a happy ending. She tries many times, often in the face of death herself- in fact, Homura never seemed to look after herself and was only concerned about others. Having a purpose she feels the need to fulfill makes her willing to endure anything, including when she gave her soul away in order to have the ability to repeat time for Madoka.
2. Time manipulation- Homura can manipulate time, which would give her an advantage to her attacks. She can freeze time and plant thousands of bombs, mines, and have several Pistol firing bullets at her foe, so when she finally unfreezes time, all attacks would decimate the enemy without the enemy ever having knowledge of what had happened. Homura uses this ability often to not only attack, but escape dangerous situations.
Bombs and guns- When she was still honing her magical abilities, Homura studied demolitions and educated herself with knowledge on machine guns, rocket launchers, pistols, and basically has unlimited control over anything that requires bullets and fires. She can summon any amount of Pistol atau bombs to her likings.
Near immortality- Essentially, Homura can never die from an attack- meaning she can be shot multiple times, endure steep falls, atau other serious injuries- the only thing that must happen is that her soul gem, where her soul is held outside of her body, must remain in perfect condition and near her person in some way, shape, atau form. If the gem gets too far away from Homura, atau the gem shatters itself, Homura will die instantly. To put it simply, Homura is like a walking corpse and the only thing that is 'keeping her alive' is her soul gem.
Not to mention her friend Madoka became a goddess of hope and Homura is being watched over sejak who is really the god of a new universe. xD
The issue with protagonists like the ones we'll be discussing is that most of them tend to be the ones who manage to come through even when the chips are down, so anda essentially have to base this off of two things - who has the most power to put someone down for good, and who can rise from being smashed to the ground the most easily and most often?
As such, we've got the big 4 - Natsu Dragneel from Fairy Tail, Naruto Uzumaki from Naruto, Ichigo Kurosaki from Bleach, and Monkey D. Luffy from One Piece. I think if we had to rank them based on power alone, Naruto wins it. Killing potential goes to Ichigo, and Luffy is probably the most resilient one on this list. Natsu is sort of a jack of all trades, managing to do well in each category but not coming up on top.
So who do I pick? I go for Luffy. I think he'd simply outlast and outdo all the others, for a number of reasons, though I'll focus on the major ones.
Having access to Gear Second, he's easily one of the fastest characters on this list, though I know that's somewhat debatable (how do we compare it to Ichigo's flash step, atau Natsu with Dragon Force?). At the very least, this puts him on similar ground to the other characters, but it also has the added bonus of massively boosting his attack power sejak doubling the strength of his hits and kicks.
He's got access to and near mastery of Haki, giving him an edge sejak allowing him to easily foresee his opponents' attacks and respond in kind. He can also make his body hard enough to take sword hits using Haki, and the force of his Conqueror's Haki is not to be messed with and all encompassing.
Lastly, he's a rubber man. Simple punches will do little to him without the aid of Haki, and while Naruto and Natsu add something to their punches, the force is going to be dramatically reduced for them. He has lebih consistent and flexible ranged attacks as a result of his Gear saat and his stretching powers as well, and his general resilience is massive. That's not to mention that he can also inflate any part of his body to giant size and then utilize his attacks, dramatically increasing his power across the board.
It's process of elimination for me. Honestly, I don't like them main characters of the 'main stream' anime, atau shonen in general. One of the main reasons is because they'll predictably win through sheer determination. There are a number of characters who I believe would win (I say Kamijou Touma kicks all of their asses), but if it has to be a series everyone generally knows, the big four go without saying, as Whiteflame already described. Why Naruto? Simple. Ichigo Lost his powers and has to get a new version each time. Luffy's not 'powerful', per se. Even after the time skip, the most powerful characters in the One Piece universe, like the admirals and the Yonkou, should still be able to wipe the floor with him. Natsu's basically as main character-ish as one could get without being overpowered compared to all the other characters in the series.
Naruto, on the other hand, is capable of using sage mode and harnessing the full power of the Kyuubi now. The Gokage count on him like an equal (he's probably stronger), the dead Gokage he fought also stood no chance, and the whole time, he fought as a CLONE. The only one's stronger than him right now are Madara and the first Hokage. Soon enough, he'll be beating them up to. Just watch.
Plus, I think he's made the most change, since he was pretty useless at ninjutsu at first, as a opposed to Natsu, who seemed to have no problem, Luffy, who was introduced as being pretty impressive, and Ichigo, who was literally transformed from a normal human to a boy with power equal to (I assume) a seated officer. So I cast my vote to the Nine Tailed Jinchuriki.
Interesting.... This is a very awesome club! Well back to the question, for this soalan I really think Gintoki Sakata from Gintama has a good chance in this. well yeah, anda may all see Gintama as not an action series but it is!
Here are my reasons: 1.He is a powerful swordsman, fast and quick thinking
2.Single handedly destroy a mobile suit(Gundam) XD
3.Has incredible endurance as seen in various battles with stronger opponents even when already beaten to a pulp he still stands and can still alih fast despite injury and kicks the enemy's butt in the end
4. Has pulled off the "Final getsuga tenshou" XD
5. Some Anime characters can destroy planets well he can destroy anime! I can't see anything else standing up against that
6. and lastly, the fact that he reaches beyond the fourth dinding he is pretty much immune to the logic inside an Anime
He's not an Anime character (yet, please don't call me on this technicality), but I'd have to go with One punch Man. It's not like it makes any sense how he could beat the strongest characters of anime. But the one thing he has that the others don't is a simple Anime law, a law that says that One punch Man wins every battle in one punch.