19" !
I put my 19" Cupra R wheels today.
Have 17" on my winter tires (BBS) and it's such a difference in the look.
19 is much more aggressive and the ride and handle is in my opinion just great.
Keep in mind to buy premium tires and not some cheap sh*t.
Did 28k in previous FR in 2 years on 18's , no problem with tyres. 54k in 15 months in Passat on 17's no problems other than usual wear. R has done 22k in 16 months and has, to date, suffered damage to 4 tyres due to pothole/road damage. Tyres are premium brand (Pirelli's although changing to Goodyear's). Its down to the 35 profile. And the crap roads.
Seriously considering a Golf R or S3 next time as they come on 18's as standard , rather than the 19's on the latest Cupra 280.