Superpro adjustable ball joints fit stock Golf and S3 arms, but not TT arms. You certainly
know these have different style (two-piece) ball joints, mate.
Bilstein B16 compare to Sachs Performance and KW Variant 3. Stock-like soft spring rates,
but better dampers and adjustability. Get Sachs Performance if you want linear spring
rates. KW V1-V3 coilovers come with progressive front springs, Bilstein B14/B16 coilovers
come with progressive springs both front and rear (and also suffer from bearing noise).
KW Clubsports compare to Bilstein CSC Clubsports, H&R RSA Clubsports, AST and the new
Öhlins Road & Track. Don't get anything else before you haven't at least considered the
brand new Öhlins.
All these clubsport coilovers come with standardized 60 mm dia linear race-type springs,
hence easily swapping spring rates and lengths.
http://www.roadandtrackbyohlins.com/