Note that I rank them based on the normal difficulity, and not the other difficulities, like Dante Must Die and others.
So in my experience this is my ranking
DMC3- I couldn't even pass the first boss at the second mission, thus for the it was the hardest.
DMC1- At least here I could pass a few missions, Although I still got stuck.
DMC4- With Nero the game is easy, very easy, with his arm mechanic. When You get to Dante's part, the game is little harder.
DmC (Definitive Edition)- Like DMC4, the game has similar grab mechanic, only for Dante. It is so easy to make combos.
DMC2- The gun button is freaking broken with its high damage. I should note that I played only with Lucia, and didn't even bother to play Dante's side since the game was a shitty game.
DMC5- The easiest game, obviously. Not only that the foes are weaker, the fact that you can revive any time by paying red orbs or gold orbs makes the game easy. Gold orbs are easier than ever to get, as there are tons of them in the missions, and you even get every day one gold orb for free!