Focus low mileage vs A3 high mileage

Hi all,

Just looking for some advise.
I currently have a budget of around £4500-£5000 to buy a car. It has to be from a car dealership as I am going through a finance company.

Couple of cars I am looking at are diesels as I am looking to get a good return on the mpg.
I have seen a focus I quite like it's done 66k miles, I would assume this is better due to the low mileage. But I have also seen a nice A3 but has done 110k miles, would people avoid this due to the high mileage or do these cars generally perform fine past this point nowadays?

Thanks for any advise!
Gary