Is UC San Diego or Columbia more prestigious?

The biggest practical tradeoff is between broad public-university reputation in science and engineering versus the brand power of a private Ivy with much wider instant name recognition. UC San Diego is highly respected, especially in STEM, research, and pre-med circles, and it has a serious academic reputation. Columbia, though, carries a level of overall prestige that is more nationally and internationally legible to the average person, partly because it is an Ivy League school in New York City.

In general perception, Columbia is considered more prestigious overall. That is true across admissions reputation, public recognition, employer familiarity, and the shorthand status that comes with the Ivy label. If someone asks this question in the broadest possible sense, most people would place Columbia above UC San Diego.

That said, UC San Diego is not viewed as a lesser school in any simple way. In fields like biology, engineering, computer science, oceanography, and health-related research, UCSD is extremely well regarded and can be seen as peer-level with very elite institutions in specific academic contexts. Among people who know higher education well, UCSD has a strong reputation for being rigorous, research-driven, and especially strong in STEM.

So the real distinction is overall prestige versus field-specific respect. Columbia has the stronger all-around prestige signal. UC San Diego has excellent academic credibility, but its reputation is more concentrated in certain disciplines and does not carry the same universal status aura.

If your question is strictly about overall prestige, Columbia is the clearer answer.