I'd suggest 'Seven Samurai' and 'Sunset Boulevard'.
When I first saw Seven Samurai, whilst acknowledging its clear quality I did think maybe it was a touch slow, and Magnificent Seven more entertaining. Saw Seven Samurai again a good few years later, and it seemed perfectly paced yet over too soon. One of those perfect films. Kurosawa must have the highest masterpiece count of anyone I can think of. Hugely influencial and copied many of them too.
That said, Magnificent Seven is very good fun.
"that won't keep us out" says the bandit refering to various ramshackle barriers the Seven have put up. "they're not to keep you out, but to keep you in"