My favorite romantic movie is: well, I have two:
The Philadelphia Story with Katherine Hepburn and Cary Grant. I love Cary Grant as a romantic lead. Hepburn is a classy lady who trumped with wit, rather than curves. Jimmy Stewart is cute in the supporting dumb role. The sprawling manor in black and white is fascinating. Everyone wore long gowns and tuxedoes, and smoked cigarettes incessantly. (Great product placement.) The father was a philanderer; the mother strong and long-suffering. Iconic characters. It is a joy to watch Hepburn’s character rediscover her love for Grant. Who wouldn’t love him?
The Thomas Crowne Affair with Pierce Brosnan and Renee Russo. The setting is modern in this remake: he is the bad boy (with sufficient backstory) and she is out to bring him down. Yet he outplays her (again with ample justification). The sex scenes in the uncut version are sizzling. The verbal sparring is never tiring. I watch it every chance I get.