Most addictive?
Three Wonders, most definitely. For those that don't know what TW is, well, it has three games on it, Midnight Wanderers, Don't Pull, and Chariot. It's a Capcom game, to boot.

Midnight Wanderers is this weird little action/adventure/shooting game (I'm not sure how to classify it), and it's kinda reminiscent of Makaimura (or Ghosts and Goblins), since they play kinda similar.

Chariot is a side-scrolling shooter, and very addictive, as well. Reminds me a little of R-Type for some reason.

Don't Pull is a puzzle game where you push blocks to kill enemies. You can also push blocks to keep enemies a safe distance away from you, and then push said block into them as they go by it. It's pretty fun.

greatest arcade game
Tie up between Vampire Savior and Rival Schools for me. Those games have a fun factor that is unmatched to me.

hardest arcade game
Gunbird, even though it's a pretty short game.