We would be getting a used car, and diesels are really expensive. There are a few current-generation Civic Hybrids for around 15k, which is just in our price range, provided we get enough for the Sonata.
The main reason for downsizing is that we have ended up with two mid size cars, when it's not very often that we need to travel with lots of people or stuff. My mother also finds that the B pillar is too wide in the Sonata (I understand it's because of the side airbags), and she sits with the seat in a position where it adds to the pillar blind spot even more.
Hybrids are really effective if you are in the city a lot, as it is near impossible to avoid speeding up and slowing down, which hybrids are excellent at making the most of. But for out in the country, diesels are better when cruising on the highway as they can run very lean.
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