Frank Sinatra or Dean Martin?
Frank had a much bigger musical body of work.
Dean had a more easygoing style and was naturally funny. Sinatra said many times that he wished he could make it look as easy as Dean did onstage. One thing Sinatra wasn't was funny. Not naturally funny, anyway.
But stage presence and musical body of work? Sinatra. But you should love Dean, too. He was one of the great Italian Americans

.
Dino had plenty of imitators. My favorite was Teddy Randazzo, a talented singer, musician and songwriter in his own right. He does a
perfect Dino imitation in one of his Fifties singles, "I Could Not Ask for More."
By chance, I put two Sinatra classics on my iPod today: "I Think of You" and "The Best is Yet to Come." I also have two Elvis's: "Blue Moon of Kentucky" and "One Night." The original of "One Night" was done by Fats Domino and has subtly different lyrics.