Ichigo, definetly ichigo cuz even if they killed him and tore his heart out just to make sure hed just go berserk on their asses cut their exremeties(arms and legs) and pop a point blank giant cero on their heads.... with just one Orihime sream XD
depends on the situation, so I'm going to run with the strongest of them all, Goku. Ichigo, even in full form would eventually "chicken" out of it and he wouldn't be able to go through with fighting because some sort of moral would leap into the situation. Naruto and Luffy really don't stand a chance against anyone who is in Goku's SSJ4 state, without dropping any spoilers here as well due to dropping this one spoiler would ruin anything people have not seen of dbgt, those who have seen it, well, if they are fighting, they aren't in peace, so, thus, Goku would soar through this. after all, Goku fights until he can't fight no more !
I would love to say Luffy or Naruto, but sadly I have to say Ichigo.
Ichigo is a Shinigami, and as you probably can remember Shinigami can't get hurt by normal mortals since they only can be hurt by different types of reiatsu in their weapons/attacks and such. So the whole fight would turn out pretty unfair since the others can't land attacks on him. x)
But knowing Luffy he would probably just invite the rest of the characters to join his crew instead of fighting, if they don't attack first at least.
Goku shifts into his constipated position and belts out a "HAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUGGGGGGGGGGHHHHHHHHHHHHHHHH" but never ends it.
Meanwhile, Naruto uses the sexy Jutsu to distract the other two as he plans an attack... and Ichigo cuts Naruto's head off with his goddamn huge penis sword.
Then, Luffy stretches his long arms to try and disarm Ichigo, but Ichigo slashes at Luffy's flexible appendages. Nothing of note happens, though, because Luffy can really freakin' stretch. Luffy then tries again to disarm Ichigo. The ensuing fight between Ichigo and Luffy consists of much hopping around and shouting.
This endless duel will keep going for four episodes.
Then, suddenly, Goku's hair turns yellow and he says "Kamehameha!" and blasts the two. They are vaporized. Super Saiyan Goku wins the fight!
...And then a beautiful phrase is uttered:
"Your drill is the drill that will pierce the heavens!"
Since Goku's power is more on a galactic scale (his attacks being able to affect, even destroy whole planets), I'd say that the fight would be severely tipped in his favor unless we're talking something like Goku in the Saiyan Saga (Or the Frieza saga so that he could go Super Saiyan, but that's kinda pushing it).
Naruto is very powerful, but he relies on hand signals and his super mode is known to be unpredictable (I'm not sure if this has been remedied yet). Plus, his mana pool is technically limited.
Luffy doesn't really rely on any kind of magic unless you count haki as magic. Even so, his physical attacks carry incredible range and his rubber body gives him incredible resistance to bladed weapons. However, his super modes can shave off his lifespan and leaves him exhausted if he overdoes it; also, there's his obvious weakness to water if the battle were to take place near a lake or the ocean or whatnot.
Ichigo is probably the most powerful between the last three, seeing as how his series is in its final arc. His super mode is easy to control and has no real drawbacks, and he can utilize both ranged and physical attacks well.
I'd probably give the match to Ichigo, since he's the one without any real disadvantages as far as I can see. It would be close, though.
As far as I remember Luffy's gear second,gear third powers suck away at his life, and since he would need to be full power, I don't see him winning. Naruto has the unfortunate weakness of hand signals, unless he goes into kyuubi form, he doesn't stand a chance. That leaves Ichigo and Goku, Ichigo has time limits on how long he can use his bankai vizzard forms (although this varies in the anime, he still has it), Ichigo's ultimate gatsuga doesn't count because it's a once off, and we all know how fucking resilient Goku is against those. Also, we know Goku can use spirit power much better than Ichigo can(even when Goku is in heaven ? and Ichigo is in seretei. That's not even comparing all the powerful transformations Goku has over everyone else. If there was no Goku, everyone else had a fair chance of winning
You can put all the anime characters you can think of in one planet, and all their powers wont mean shit when Son Goku destroys the planet with a Genki Dama ball. And I highly doubt it if anyone can even withstand his Tenkaichi....