You can do both.
If you top your plant, you will lose your main cola, but the rest of the plant will have energy diverted to it, top it when it reaches the desired height for your grow space.
I LST every time I grow, bending the branches to create an even canopy across the top. The idea is to allow the buds to have equal ammount of light so that they can grow evenly.
Normally your plant will grow tall so the top has most of the light whilst the bottom branches receive less.
Here is my LST'd & topped northern lights to give you an idea -
and a more recent pic -
I put a rubber band around the base of my pot, tie some string around the branch and hook the string through the rubber band and pull it down a little at a time, this means I can make my plant fill my grow space to maximise yield
hope this helps.
good luck