Seeing I owned a Manual MK5 GTI for around 3 years and did the better part of 65,000km's in it.
Had a MK5 TDI DSG, for 6 months and did around 25,000kms in it.
I now own a MK5 GTI DSG myself (Well the girlfriend also has a DSG GTI) only for around 6 weeks and already done 6,500km's in it as well.
My DSG GTI is far more economical than my manual GTI ever was. Even with the DSG being Stage 2+ as well.
I have done the same 1500km's round trip in my GTI as I did in my TDI, both's fuel consumption were/are identical, 650km's per tank.
Over here in NZ you have to pay road user charges on top of the diesel pump price (per 15,000kms). Then if that's not bad enough, if you drive a diesel or hybrid car.
Your yearly registration cost are almost double compared to standard car. So over here it made no sense to keep my diesel and simply just get another GTI.
Either way, go drive both. A DSG equipped car you really need to drive for a few hours at least (if you have not ever owned/driven one). then compare the DSG vs manual debate to yourself. Then select which ever one you prefer. Regardless of what any of us say. I have owned both, given the choice, I would always pick the DSG over the Manual.
But hey, thats just me. Everyone has there own right to their opinion.