There are generally two types of muscle fibers in your body, slow twitch and fast twitch.
Slow twitch muscle fibers cannot exert as much force as fast twitch, but can sustain an effort over a much greater period of time. (Muscular Endurance)
Fast twitch muscle fibers can exert a great amount of force but for a very limited amount of time. (Muscular Strength)
I personally like to focus on both. In my opinion it's better. It gives you a more even body, rather than all strength but crap stamina, or all stamina and crap strength. Best of both