I prefer mocknecks...turtlenecks just come up too high for me. But--I want the mockneck to actually stand up around my neck! I've had too many--mainly heavier sweaters--where the neck actually lays kind of flat like a crewneck.
I prefer turtlenecks although mock necks are probably a better choice with my short neck. I also like funnel necks and think they often look better than mock necks too. To me, mock necks look like the designer/manufacturer took a shortcut.
I prefer a turtleneck. I like the material to cover my neck completely. I own several solid turtlenecks in various colors and weights. I like wearing my turtlenecks under blazers or leather jackets with jeans and boots this time of year. That's a classic timeless look I love.