OP here, surprised to read how most everyone would take 7.5R over MK8 GTI.
Appearance wise I strongly prefer the MK8 GTI exterior over the MK7.5. The MK8 interior, not so much!
Best interior to me belongs to the MK6 GTI Wolfsburg Edition. It seems VW cheapened the interior of the MK7, and may have cheapened it even further with the MK8 GTI (based on videos).
But VW may have directed their money on engineering and tuning instead. Plus it will assembled in Germany once again!
In regards to price, I'm predicting 8-12 months from now, an '18-19 CPO Golf R would average $32k, with the new MK8 GTI S going for $30k. But who really knows.