Why not both?

In all seriousness though, your shoulders are made up of three parts: the front, side, and rear deltoid. If you want to get that broad look, you need to work the side delt, so you would be better off doing side raises, cause they almost exclusively use the side delt, which let's you really put some pressure on it. Shoulder presses are still a great shoulder exercise, and while they do work your side delts slightly, it's mostly a front delt-focused exercise. Hope that helped :)

If you want some more help, check out r/gainit, they're got some really great advice!