What is the difference between the Audi A1 and A3 engines?

I am interested in purchasing an Audi A1 or A3 but I'm not sure which engine option to choose. Can someone explain the main differences between the two engines and which one would be better suited for city driving?

The Audi A1 and A3 have different engine options, with the A1 having a smaller engine and the A3 offering larger engine options. For city driving, the A1's smaller engine would be more fuel efficient and cost effective.