If you are after my favourite visual novel that would easily go to 車輪の国、向日葵の少女. Never could put my finger on the reason I enjoyed this title so much besides the fake tsundere, Touka.
Other titles I am quite fond of:
G線上の魔王 - Haru route is quite possibly one of my all-time favourite routes in any visual novel ever, especially that epilogue.
穢翼のユースティア - It's a goddamn shame this never got completely translated as the base medieval setting, character development, et cetera were really enjoyable to read.
鬼哭街 The Cyber Slayer - Cyberpunk done right, especially considering it was the first of its kind for the visual novel market.
戦国ランス - Rance is just full of charisma which makes this series really enjoyable despite how depraved it might be.
"Fluffy" titles I tend to lose motivation in following if the comedy isn't decent or the characters themselves are bland.