The Volkswagen Golf would be cheaper to buy and run but the Audi A4 Avant is nicer inside and out. Skoda Octavia is certainly not to be sniffed at. It's a good car but you get what you pay for. You don't need a diesel if you're covering 10,000 miles per year. There's not a lot of choice out there because when purchased new these cars were more popular with a diesel engine. 1.4 TSI VW Golf or 1.8TSI Audi A4 Avant petrol engines. Avoid DSG or as Audi call them S Tronic auto gearboxes.

Have a good look at a petrol manual Octavia estate, Strawberry, The plastics may be a little harder than in an A4, but they are just as sturdy and will last a long time. I had three Octavias and to me at least they didn't feel any cheaper inside than the Golf estate that preceded them or the Audi Q2 I have now.

The best engines are the 2.0 petrol in the vRS and the 1.4 TSI.

Your existing car is of an older design and likely less susceptible to problems (mainly the DPF, but others too) associated with using them for short trips from cold - modern diesel HATE this sort of journey and that's why for someone doing under 20k miles a year would recommend a petrol engined car unless very heavy loads (towing etc) were carried very regularly.

Don't forget that a diesel engined car will be more expensive to buy, service, insure, and, if some major component fails, fix. You'd only make your money back if you did well over 20k miles a year made up of longer distance, 60mph+ driving. Modern petrol engined cars (standard ones, not high performance) are more reliable than modern diesels because, up until now, they didn't have much complex emissions control devices and are better suited to urban driving.

Given you seem to also keep your cars for a long while, or buy one out of warranty (and thus well under 50% of its original RRP) and sell it when its very old, low depreciation won't make much of a difference when it comes to selling a 12yo car. If you want to only consider VAGs (don't get a DSG auto - they are unreliable for engines under 2.0 ltrs, average for ones of 2.0 and above and aren't suited to town driving), perfhaps you could consider a SEAT Leon ST 1.4 TSI 150PS. You should be able to get 45+ mpg average and its a decent performer.

If you are concerned with driving in a rural area with poor quality roads that is reasonably hilly, regularly sees bad weather and a reasonable amount of snow (not cleared/salted), then whatever you get, I'd advise either getting it shod in all season tyres or, if you have space to store them, a set of winter tyres (and possibly steel wheels [check with the dealer as to what is allowed - some winter tyres can only be matched with smaller wheels and thus need to be higher profile than the summer ones to compensate) in addition to the summer ones on the car as standard. Far cheaper than getting a 4x4 which can be expensive on the jungle juice and repairs should it go wrong, and often grips better in really poor conditions in winter.