Okay, if we're gonna lay it all out, then I think Warriors Orochi has the best gameplay mechanics, and the most satisfyingly insane storylines and dialogue
Mitsunari Ishida: "Hey Pang Tong WE SHOULD TOTALLY HAVE KIDS TOGETHER"
Pang Tong: "I KNOW RIGHT THEY'LL BE AWESOME"
Plus the ludicrous number of characters, the addition of sick R1 attacks and air dashing, and then the addictive weapons upgrades... All excellent enhancements to the game.
BUT. But but but but but. My best memories of the DW series, as a whole, come from playing DW3: XL with my bro. I suspect it will always be so.
Additionally, I gotta say DW3 had the best character designs for most characters. That's my favorite Zhao Yun right there.