OK, here are the differences.
If you head to the Main Entrance Plaza, you can clear Security at the Sephora entrance before park opening, and take your time. At park opening, more than two park turnstiles are open for Disney Hotel Guests to enter the park under the Extra Magic Hour.
As for the direct GCH entrance, while it is true it is now just GCH guests that can use the entrance, the design of it only allows for Security to start checking folks at park opening, and then there are only two turnstiles, so limited entry that can delay your start, depending where in the line you are at.
But the faster way is clearly the Main Entrance gates if you want to be in the parks first thing when they open.
30 minutes into the day, I would opt for the direct GCH entrance, as there should be very little wait by then.