DMC1, the reasons:
- enemy design
- enemy moveset
- environment
- theme
- perfect difficulty progression
- DMD didn't try to raise the enemy's health while lowering yours only, but they give the enemies bigger moveset, access to their invincible DT mode, & different placement of every single enemy
- real DT, instead of just raising your stats
- not having a mission select screen contributed to the creepy & difficult feel of the game
- Secret Missions themselves
- Secret Missions placements were actually "secret"
- memorable weapons, like Nightmare Beta
- the coolest pause screen in a DMC game
- Dante was believable, AND he was badass
I don't feel like I need to add more, so I delivered my point.