There's an extra risk when buying a used car, in that you don't know how it was driven. I've been in brand new rental cars with only 10-20k on them, and they were already showing signs of abuse and future problems. A used car with 20k on it could be fine, or it could have some sort of major underlying problem caused by serious abuse that you don't notice until it's too late.

If you're looking at $40k+ brand new vehicles, and lightly used models go for $35k, I'd buy new. On an investment that large it's worth a few extra thousand to eliminate the risk.

I have nothing against used cars either. If you're looking on the lower end, absolutely buy used. When I bought my current truck it was 14 years old and had 120k on it. It's been my daily driver for years now and has never had a single problem. Certain models last a very long time with proper maintenance, and are best bought used. It all comes down to added risk vs money saved.