Is a PhD degree from a European university considered equally valuable as one from the US? I earned my PhD in continental Europe. Except going to a few conferences outside Europe, my network, collaborations and events were all in Europe so I was pretty much living in a European bubble. I am still here, but now that I am in a faculty position I started collaborating with people from everywhere and travel quite a lot outside Europe. As much as I try to avoid generalizing and I am aware that much is field dependent, there are some things I noticed about the general perception of European PhD degrees (and this can probably be extended to universities in general) outside Europe:


Students from Asia (especially from China and Korea) I met said that they prefer going to the US for a PhD, and Europe is only a second option because of less prestige.
When I was considering applying to positions in the US, a few people told me informally that I don't have good chances as those who apply with PhD degrees from US universities, without even considering my CV.


But my experience is conflicting and makes me confused:


I visited a few universities in the US, and noticed that people doing a PhD are treated as students rather than as employees, financially they struggle and most of them have to work on stuff other than research (taking courses, teaching). Frankly the whole system looks miserable to me. In many European countries they would be employed with a decent salary and benefits, focus only on research, have a better travel support, among other benefits. If one was given the choice between the two, I don't understand why anyone would go to the US to do a PhD instead of Europe (no hard feelings) and consider it a better option.
Judging from job applications I get from fresh PhD graduates around the world, on average those with a PhD from the US are not better than others (I am aware that this might be biased because good PhD graduates in the US often prefer staying there).
American PhD theses I have seen are not as good as those from Europe. For example, in the Netherlands most PhD students must publish a few journal papers before they graduate (some have 4-5, and this doesn't include conference papers). The theses are usually of high quality, and are even published as books. Looking at recent PhD theses at elite US universities like Stanford, Harvard, Berkeley and MIT, I cannot help but consider them less good and with less contribution.


This will likely strongly depend on the field, but in general I find that the average PhD experience, student wellbeing and quality of work in Europe is no worse than in the US, if not better. Yet, people worldwide seem to favor US degrees.

Is a PhD degree from a European university considered equally valuable as one from the US?
If not, why is there this gap and lower perception of PhD degrees from Europe?
One simple answer is no, the two aren't equally valued, because the two are also not even regarded as equal.  As a trite example, consider that many European countries (especially the German-influenced ones) are very picky about which letters you can put before or after your name.  I have a dual-degree, so I am "allowed" to use Dr. as a legal part of my name in Germany; but my officemate with a solely American Ph.D. cannot.  The way in which doctorates are made is also vastly different-- the U.S. requires coursework and then research, (often) mixed with lots of (often underpaid) teaching duties, while European doctorates typically frontload on the research and are light on teaching responsibilities.  Those different experiences produce different palettes of qualificiations and skill sets.  It's no wonder that if you're primarily paid to do research, you'll probably produce a better thesis than someone who had to perform teaching duties 20 hours a week.

However, there's also the danger of regarding "Europe" as a monolith.  I've heard anecdotes from some Italians who struggled to get funding to finish their degrees without taking on big teaching duties. (But see comments by @MassimoOrtolano.)  Croatia, Romania, and Bulgaria all suffer from "brain-drain" as young folk go west for education.  And I get the sense that when people say "Europe" in the context of academia, they're almost always, knowingly or unknowingly, referring to Germany, France, and the UK.  Few other European entities have as much economic, political, or historical influence as those three.

Along the same lines, Europe comprises dozens of different languages and cultures.  Asian students are more likely to already know English than French or German (or Dutch or Polish or Finnish...) and therefore will seek a degree in an English-speaking country.  American culture and accents are more familiar to the world than, say, British or Australian, because of the movie and music industries.  (The UK is also not super stable in terms of immigration standards at the moment.)  Seeking a degree in the U.S. is then just plain easier-- you don't have to spend time learning a new language or adjusting to a new culture.  For these students, it may be that because English is the de facto language of science, the notion of what's considered "prestigious" just followed blindly.