I always had much success with trimming the lower branches. I top early to get many tops, than lollipop just before flowering. You end up with a mass of colas which in the end, end up much easier to trim and you get better smoke. I have a video on my youtube channel that shows you what I do when I top and lollipop.

Lollypopping your plants to get maximum airflow and bigger buds on your cannabis plants - YouTube

Happy growing