I would say both companies produce great products. The one thing I would do is compare wattage to wattage. The GSL 602 draws 350w for an advertised price of $1,599. That is $4.57 a watt. The Advanced 360 Draws 390w (I tested mine) with an advertised price of $999 for a cost of $2.56 a watt.
They are both quality systems. They use different naming conventions though. The GSL calls theirs a 600 (now the 602) because it has a total chip wattage of 600 watts (but draws 350w). The Advanced has a total chip wattage of 864w but is designed to draw 360 (but closer to 400w) so they name theirs the 360. So if you want to compare apples to apples, then the GSL should be called a 350 or the Advanced should be called a 864.
Just some more information for you to make your decision. And this is no way intended to "bash" anyone else's lights. I have seen the GSL perform very well in JZ's grow and I had good results with another manufacturer's lights my last grow.
Most importantly, both GSL and Advanced are
sponsors here. So whenever possible, support those who support us!