I'm sure you will hear many opinions, but I will point out a few. Pulling from the outside can increase the bug risk in your grow. You can get a filter to prevent this, but the risk is still there. If you keep your living space cool, then pulling from the inside can help if your outside temps are hot. Some people get caught growing because the exhaust outside with a crappy filter or no filter at all. Don't be that guy. Depending on where you are growing at your place, you might have to have ducting going every which way, which can be very frustrating. Both outside and inside have co2 and fresh air, so no need to worry about that.