Buying advice needed for a high mileage driver

Looking to get a car to last 4/5 years, I'm a high mileage driver approx 600 miles a week and 90% of my drive is on motorways. I've found two potential cars that's within my budget, but would like to get some thoughts if they are good choices.

Audi A3 2011 2.0 (£10000)
1 owner
Diesel
45000 mileage

Vauxhall Astra 2014 1.6 (£8400)
1 owner
Diesel
18500 mileage

I'm swaying towards the A3, as I do like them as a car plus friends and families have had one, they never had any problems with them.

Thanks in advance.