Unfortunately, options are pretty limited if you want 100% fitment. Been searching myself for a while now and I've settled on the TCR.
OEM Level
- Oettinger $$$$$*
- Clubsport (requires a standard Golf hatch...incredibly expensive for GTI/R owners) $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*
- Golf R PP/Rabbit spoiler extension $$$
- TCR rear spoiler (similar to the PP/Rabbit spoiler but slightly bigger) $$$
Aftermarket w/ 95-100% fitment
- Maxton $
- Aerofabb $
- Aggressiv (probably closer to 90% fitment since you can see a sliver of the OEM paint on the side) $$
- iSweep (not completely sure on this one, everything I've seen seems to indicate minimal work needs to be done for fitment) $$$$*
- A Spec PPV400 (Very expensive $1000 and not sure on fitment since you don't see them around that often...I would hope that for $1000 it at least fits close to 100% though) $$$$$$$$*
- OSIR $$$$$*
- SRS Tec $$*
Aftermarket w/ 0-90% fitment
- All of the various replica and 'custom' spoilers available on the aftermarket via AliExpress, ECS, eBay, etc. Literally dozens of various spoilers that can run the gamut in terms of quality/fitment.
Mountune (M52) is going to be putting out a new spoiler extension, not sure how it will fit since it's not out yet but looks decent from the pics. But that may be another option in the future.
* May require paint which could make things more expensive. Some will definitely require paint since they come unpainted and non-carbon fiber. So make sure to factor in some money for that.