I've always thought BUTCH CASSIDY was entertaining but unmemorable (save for the ending and the jump off the cliff) and got a HUGE boost from its considerable star power. I much preferred the later pairing of Newman and Redford, THE STING (though one could argue it's not as good as fellow Best Picture nominees CRIES AND WHISPERS and THE EXORCIST -- could we have a STING V EXORCIST episode..?)
I didn't see MIDNIGHT COWBOY until it was re-released in the 90s, but didn't feel it dated very badly. I find it very moving and affecting, and it's filled with many terrific little moments: "I'm walkin' here!", Voight and Hoffman shuffling in the cold to the orange juice commercial jingle, Hoffman's bizarre daydream of hitting the big time in Florida. But my favorite moment in the film -- one that has stuck with me over the years and that I think of often -- is when Voight is walking by the coffee shop, spies Hoffman through the window, and these two desperately lonely souls share a brief, warm smile. Quickly followed by Voight's smile fading as he demands his money and Hoffman digging through his pockets for change, comically pleading "I want you to have it!" Delicious moment in a terrific movie.
MIDNIGHT COWBOY hands down.