Buying a New Car
When buying a card, the two things I cared most about were reliability and price.
A car's reliability can be estimated based on the model's historical data and on expert predictions of the current version's reliability. For the former, I used data collected by Dashboard Light Dashboard Light and for the latter I used Consumer Report Consumer Reports and JD Power JD Power ratings.
A car's price is largely computed by adding its sticker price to the discounted cost of expected gas expenditures. Other things matter too but typically don't change the relative estimates much.
For instance, insurance premiums typically scale roughly linearly with car price while oil-change costs are typically small and similar between cars. Maintenance costs also matter, but that is also implicitly included in the "reliability" bit.
Accounting for these factors, I examined a ouple dozen models and found two that stood out as both cheap and very reliable: the Honda Fit and the Toyota Corolla. Based on historical data, both are top-tier in reliability, while the 2020 Corolla is rated slightly more reliable by experts. On the other hand, the Fit was slightly cheaper.
Other factors obviously matter as well like safety, comfort, space, and handling. Personally, I find most modern cars sufficiently comfortable, and I've never really been annoyed by a car's handling. I do care about leg-room, which Edmunds provides on their site Edmunds. Most cars have 40-43" of leg room for the front seats, but room for the back seats varied quite a bit between models. Fortunately, both the Fit and the Corolla had ~40" each.
Safety is a concern I should have. Fortunately, both models had prefect or near-perfect scores on government National Highway Traffic Safety Administration and nonprofit Insurance Institute for Highway Safety safety tests.
Safety testing for cars is not perfect since it is generally based on crashes between cars of similar sizes. For this reason, small cars like the Fit and Corolla are actually more dangerous than the tests suggest. However, that extra danger is exclusively due to the zero-sum arms race to own a bigger car than "the other guy" for self-interested reasons (status, safety, etc) and I don't want any part in that anti-social endeavor.
I ended up buying the Toyota Corolla, and, to the best of my knowledge, it and the Honda Fit are the cars that best fit the needs of practical people without families.
Next time the question of which card to to buy comes up, I'll try to link to the data I compiled.