Buy a GT for you, a GTL for her (or him) on the back unless that person is small, then it may not make much of a difference. I have a GT and the rear seat could be bigger and I am moving from a GT Box to a GTL box for her comfort and having to get a new grid for the box to be moved to GTL position.
Get the right bike that meets your needs instead of correcting or trading it in later.
It all comes down to use, what you think you will be using it for...a GTL will be much more comfortable for a passenger on a long trip/ride. The GTL has better passenger comfort/space, so if that is a top priority then stop looking at the GT completely. A GT would be better for 1-up sporting rides. A GT should be fine on shorter 2-up rides, body type of the passenger depending for longer rides.
Better to try them all with the passenger to find out before you get the wrong one. Some ppl love the bagger, some not so much...it's hard to compare as they are radically different setups. The bagger will not handle like the GT or GTL, so if you want more "sport/handling" then the bagger is not for you. Don't go by looks alone...you may like the look only to find it doesn't perform as you thought.
Lots to think about...the test rides will help immensely.
CJ