I am still waiting for delivery so I cannot compare gti vs 135i!
I can briefly summarise my 135i experience after owning one for 18 months.
For--straightline speed, v. practical for a small coupe, decent residuals, excellent customer service from my local dealer
Against--Starting to develop a few electrical gremlins and it doesn't cope very well with my local road. Those turbo do drink petrol---the combined figure is a joke! Sat nav is a waste of
money!
My replacement car need to be more comfortable, reliable and cheaper to run as I do more than 10000 miles a year. My mum drives a mk5 gti so I got a brief idea how good a gti is. Test drove the Mk6 with the ACC and 18 iinch and I was hooked. Just like a 911, it does everything perfectly!