To be frank and honest, my answer would be more about my attraction to opposite gender, so I would spend the day with Yamato.
But if we're talking in general terms, I would like to be with Sanji.
1. Guaranteed delicious meals from breakfast, lunch, supper, and dinner. As a poorfag, tasting free star level chef is a blessing. (~3 hours)
2. Can bring me to fly in the sky. (~1 hour)
3. For the rest of ~20 hours, I'd ask him to Blue Walk across Bermuda Triangle to find it's mysteries and treasure hunting in the depth of the ocean. Satisfy my curiosity and potentially bring me $$$.