My swing speed is about 42～43m/s. Which is the better for me 10.5 or 12 loft?

in the US we are measuring swing speed by miles per hour (MPH). I converted 43 meter/second, it is 96 MPH. 96 MPH is a good swing speed. For a golfer with 96 MPH I would suggest 10.5º. But this is only one factor. The other factor is the Stiffness of shaft and the location of bend point or kickpoint in the shaft. if your shaft has the bend point in the center or towards the butt, it will reduce the actual loft. if your shaft has bend point in the tip section, it will increase the loft promoting a higher ball flight. Please visit a clubfitter with swing analyzer and launch monitor.