What's the best used, small, automatic car?

I'm looking to buy a used, automatic, small car for my 22-year-old son. It will be his first car and our budget is £3000 - £4000. Ideally it will be a low insurance group, but I mostly want you to recommend...

What small automatic would you recommend?

I'm looking for a small automatic car which could be a petrol hybrid. Probably a year or 2 years old, what would you recommend?

Should I buy a diesel when I only do 5000 miles a year?

I am looking for a car, preferably diesel and automatic but essential it is comfortable. My budget is under £20K what would you advise. My annual mileage is low around 5000 so not concerned on fuel costs.

Automatic for a nervous learner

My 20 year old daughter is learning to drive and despite numerous lessons is really struggling with manual transmission. She has suggested trying an automatic but I am concerned about the implications....