Hi-
B&G is mostly a glute workout, GS Legs is a wellrounded "allover" leg workout, so it depends on what you want to focus on.
When I first got B&G, I did it 1x/week for about 8 weeks in a row..love it! The upside, my butt and hamstrings really saw some good improvements. The downside is that I lost strength in my quads and definition in my calves. ( I only work legs 1x/week so adding another day of leg training isn't in my cards.)
The upside of GS Legs is that it hits a little bit of everything and is fairly challenging too.It has a great variety of exercises, so the fun factor is definitely there.
I do think B&G is harder, but mostly because so much of the focus is butt/hammies, with not alot of rest between sets.
There is also the ab workouts in B&G which while aren't my favorite, are pretty decent.
Make sure you post to tell what you decide.. Really you can't go wrong w/ either, but they definitely have different focuses.
Take care, Lynn M.