Aside from DmC Devil May Cry which I have yet to fully play through, Devil May Cry 2 still remains my favorite out of the original five. No joke. Devil May Cry 4 Special Edition is a very close second. Story aside, the main reason why I loved #2 so much appears to be the same reasons why a lot of people seem to dislike it unfortunately. I found it to be the easiest, therefore I enjoyed it the most. The amulet system was nifty though but the Sin/Majin Devil Trigger was a nuisance to pull off. I do miss Lucia though, even if she was rather depressing. Can't blame her though.
I just didn't enjoy the character direction in DMC 2 or DmC, which is a big factor for me personally in my character action games.
DMC 1, I enjoyed but definitely enjoyed other DMC games more. Clearly it's a foundation that was built upon & improved over the years.
DMC 4, I am torn on. The combat is really good to me, the Devil Bringer adding a lot of fun. But half of the game getting repeated again as Dante, including bosses being fought again was a let down for me. The proud souls as a separate currency felt like an unnecessary change. I know the devs were trying to consider western audiences to make it easier. But as a western player, I didn't mind what previous games did. Also that boss fight where you grab swords & throw them at a window wasn't great either. Overall, it's still a fine game though.
DMC 3, I recently finished & absolutely enjoyed. At times I could get lost on where to go next. But the combat was very satisfying & the characters were very enjoyable. I like Dante's characterization here more than what he was in DMC 1 & 2. Vergil, Arkham, Lady were all fun characters that I enjoyed seeing go through the story. Nevan was a bit tedious of a fight, but my complaints with this game were very minimal.
DMC 5, I haven't finished, but I'm 25% through the game currently. So far, my only possible negative is I don't like playing as V as much as Nero. I imagine I will enjoy Dante more than V as well. It possibly could become my favorite DMC game, but I'm not sure.