Glowstone provides a luminescence of 15, whereas torches only provide 14. However, placing the glowstone block in the ground reduces the area that it lights up to that of a torch, whereas placing a torch on the ground lets it provide maximum light while still remaining flat to walk on, just not to look at.
It all comes down to choice really. Do you mind looking at torches sticking out of the ground, or are you willing to use as much glowstone as you need to keep it lit?
Light loses one level per block traveled from it's source. Mobs spawn at light levels of 7 and lower. This means that if you were to place torches (or glowstone in the ground), you would be required to place a torch every 15 blocks (leaving 14 torchless blocks) in order to keep mobs from spawning, while using the least amount of resources.
O = Torch
+ = Block
Should keep monsters from spawning (if not, leaving 13 torchless blocks will)