Do you like playing on the easiest difficulties? Sigma and Razor's Edge both have EZ modes. Sigma has Ninja Dog mode which weakens enemies and bosses and gives free healing and support items. Razor's Edge has Hero mode which is a literal god mode because you do automatic blocks and dodges and will never die. The latter may sound incredibly boring because it removes all sense of difficulty but if what you're after is seeing what Ryu can do, that might be your best bet but you do still need to gather Karma to upgrade his moveset. I believe performance is the only difference between Wii U, PS3, and Xbox 360, as in, it runs better on the other 2 than Wii U.
If what you're after is an "easier but still challenging so it's not boring" difficulty, Sigma is the way to go. Ninja Dog mode is still quite challenging for people who are not used to playing character action games even with all the healing items you can get.
Sounds good; I've played the Devil May Cry games, though I've generally played those on Normal difficulty and using a guide to find health upgrades - I feel like Ninja Gaiden would be closer to playing on Hard mode, though I'm just making assumptions. (I've also played the Bayonetta games and Metal Gear Rising, among other Platinum titles, so I have some familiarity with character action games)
I'll look into Sigma on the PS3 and give that a shot, assuming that the price is right. From what I've seen, it seems like blocking is going to be a key component, so that's something that I'll have to get used to. (I'm used to dodging, like in Bayonetta and with DMC3-5's Trickster style, and I basically never block in fighting games, so I'll have to adjust my playstyle)
EDIT: I got Ninja Gaiden Sigma - just need to wait for it to download, and I'll see how it goes.
EDIT 2: not off to a great start. I beat the first chapter without dying, but the second chapter introduces wizards that can appear out of nowhere, hit you with a four-hit combo or a homing projectile (often while you're mid-combo or dealing with another enemy), and then vanish. That was enough of a pain, but then the game introduces enemies on horseback that are more mobile than Ryu and have a longer range than him. I assume I'm intended to use the bow, but there doesn't seem to be a lock-on function, and I doubt I can hit the horsemen when they're moving at that speed, I have five arrows (more if I check the nearby corpse), and there are at least six horsemen who show up one after the other. (I'm not sure how many there are in total - every time I beat one, another one immediately shows up)
I get introducing maybe two or three horsemen to give you a chance to fight them, but this is throwing way too many of them at me at once, and the wizards feel like an endgame enemy thrown into the second chapter because the developers seem to think that this is the arcade era where the only way that a game can make money is if it's insanely difficult to beat.