I'd go for the ED30 if you can afford it.
I think you'll do well to find even a GTi with Xenons as the price of the option was so high not so many people ordered them.
Regardless of future tuning potential the K04 engine car with DSg is a lovely drive.
I also share your thoughts on the Cupra, not for me at all. Yeah ok so it's cheaper but for a good reason. We have a Leon TDi and it really doesn't do it for me.
Some I picked out for a friend earlier today from a trade website are -
VOLKSWAGEN Golf Hatchback Petrol - 2.0 GTi 5dr Auto (Tiptronic)
0707 MILEAGE: 32,000 Miles 1 owner Black
Distance: UNKNOWN
Full franchise service history Parallel Import
Additional comments: Reg/Chassis No: YX07 JZE / WVWZZZ1KZ6W042346. Number of keys available not stated by dealer
PRICE: Buy it now for £13000
VOLKSWAGEN Golf Hatchback Petrol - 2.0T FSi GTi Edition 30 5dr Manual 6 Speed
0707 MILEAGE: 38,000 Miles 2 owners Silver
Distance: UNKNOWN
Full franchise service history UK Car ABS, Air conditioning, Alarm, Alloy wheels, Central locking, Electric windows, Front & Rear parking sensors, Half leather heated seats, Metallic paint, Power steering
Additional comments: Reg/Chassis No: WVWZZZ1KZ7W267183. Silver/Half Leather/Tartan Interior Limited 30 Edition, Allow £150 - £200 Prep.. -- Number of keys available not stated by dealer
PRICE: £13,750
VOLKSWAGEN Golf Hatchback Petrol - 2.0T FSi GTi 5dr Manual
0656 MILEAGE: 43,000 Miles 1 owner Metallic Grey
Distance: UNKNOWN
Full franchise service history UK Car ABS, Alarm, Alloy wheels, Central locking, Climate control, Electric windows, Metallic paint, Single CD player
Additional comments: Nice car 3 wheel edges need refurb -- 2 keys available
PRICE: £12000
VOLKSWAGEN Golf Hatchback Petrol - 2.0T FSi GTi 3dr Manual 6 Speed
0656 MILEAGE: 44,000 Miles 2 owners Black
Distance: UNKNOWN
Full franchise service history UK Car ABS, Alloy wheels, Central locking, Climate control, Cruise control, Electric windows, Factory fitted phone, Front & Rear parking sensors, Full leather heated seats, Power steering, Xenon headlights
Additional comments: Reg/Chassis No: MJ56 CZG / WVWZZZ1KZ7W086702. full leather 18" monza -- 2 keys available
PRICE: £11800
Sadly only one DSG and I have no idea how the prices compare to current retail, I've not checked.