Goodfellas is by far his best work and a timeless classic, that film will be watched in 50 years and people will see how real gangsters were.
Casino was dragged out and held up by Pesci imo, good film but no Goodfellas.
Taxi Driver was shit when I watched it but I get a feeling everyone who loves it is in the old category that grew up with it, to me it was just a weird guy struggling with PTSD or whatever.
Wall Street was well made but dragged like a bastard, the story to me was just boring but I guess what can you do with a story about a guy who makes money?