Buying a GOLF/A3/LEON

[ErUpe]

Hello ladies and gents. Long story short I'm thinking about buying a diesel VAG and have 3 options within my budget 

Golf 6 (1.6, 2.0)

A3 8P (1.6, 1.9, 2.0)

Leon 3 (1.6, 2.0)

I'm wondering which engine is a better choice and which engine revision(year) is better. I also wonder what things should I look out for regarding mileage and what should I expect in terms of servicing in future, considering I change oil every 5-7k miles and flush radiators every 2 years. I'm trying to be realistic so any advice would be really helpful.

Thank you in advance