I am interested in hearing more about the new 7 speed DSG, which should be the same between both. New owners have been reporting it isn't as responsive or crisp as the 6 speed DSG from the MK7.
Since they are now virtually the same car, for me it comes down to: "Am I willing to pay a bit more for a hatchback" as the GLI will apparently be a bit less costly than the GTI.
I imagine the similarities between the 2 in terms of driving will be considerably similar, and differences minor. So hone in on those differences (trunk vs hatch space and usability, rear seat space, differences in any driving dynamics, do you like saying GTI or GLI better
).
Also, I hope the 2 versions you sample have the same transmission in order to eliminate that as a variable in the testing.