MY TWO CENTS
Get the DSG. I went from a mk 6 dsg, to a mk 7 dsg but thoroughly tested the manual before opting for dsg once again.
First the DSG is the better more polished option and the car feels like it was designed around that transmission. If the GTI had a really good manual i would have gotten it, but as far as manuals go...it's just not that great. The throws are somewhat imprecise, and the clutch is vague.
If it were a Honda or bmw manual from say 10-15 years ago, i would consider going manual. The DSG is 90% as engaging(my opnion), and you can still shift the gear selector (just not muti direction), or use the paddles. In essence the DSG gives you 4 different ways to drive, normal sport, paddles, shift the gear selector.
DSG handles more power if you tune as well, and is faster stock vs stock. There also seems to be some mechanical failings with the manual ("crank walk"). JR14 on youtube just roasted his whole engine (being a bone head) but supposedly crank walk was the issue. DSG has been around for a while now and is a very reliable transmission for what its capable of.
Manual has only 2 advantages. Bragging rights with the cool kids who insist manual is the only way to drive, and slightly more engaging. The second one is subjective, and all depends on what you like. Personally i like that the dsg is going to give me what i want pretty much every time, once you get comfortable with how it behaves. No missed shifts, stalls, jerking all the time etc.