I think guys like both, as long as the hair is healthy and clean. I've heard some guys say they like me better with straight and some like me better with curly but I wear it however I feel like it, especially if I'm running late. Straight hair is sleek and elegant and curly hair is cute and innocent. Wavy hair is fun and flirty. As long as the curly hair isn't frizzy or anything (use some styling product like moroccan oil to make it smooth and shiny) I don't think it matters as long as he's attracted to you. If your hair is stick straight instead of a curling iron you could just try a scrunching gel, scrunch your hair with the gel in your hands and let it air dry.
This is a good example. I think both ladies are attractive, but I do like the one with the straight hair a little bit more. Plus she's a brunette, so maybe I'm just biased :) Plus I find Salma Hayek to be really pretty too, so I don't know lol