I would drill toward the top near a corner, and preferably in the rear of the tank. I think 2inches from any edge is the rule of thumb to use.
The reason is that if you have a standpipe inside the tank, and happen to bump it while working, it really torques the glass and will almost certainly break it....I tried that approach twice myself before learning my lesson.
If the standpipe is external and toward the rear of the tank, it is less likely for you to knock it around while working. That lowers the risk of a break in the tank.