What's the best place to be for an atheist?

France, in my opinion. In France, freedom of belief is protected while the state is required to remain neutral and to limit religious expression in many public institutions. Moreover, France restricts public displays of religious affiliation in various situations. Public school students cannot wear conspicuous religious symbols while public officials must maintain religious neutrality while on duty.

Here’s a table comparing the US, Russia, China, and Iran in this respect:
Imgur

What are your criteria here? It is hard to judge these things from gross statistics.

France retains a significant Catholic cultural heritage despite the efforts of the Revolution. Though, the state does not recognize any religions and none of your tax dollars will be funnelled to them, and the existence of the odd cathedral should hopefully not cramp your style. Even in countries like Czechia, among the national holidays are ones like Christmas, though that could be historical baggage that has not been dealt with yet.

Really, though, would you rather be an atheist in France or Sweden, or an anything in China (though I suppose that, in some sense, atheism is a state religion in China)? As for the US, it might depend on where you live in terms of people getting asked about their religion or otherwise having to deal with religion at all; the picture is not as rosy as your table suggests.

I am not sure why Iran is on your list— it is officially an Islamic Republic right now.

Exactly. In the U.S., living in a liberal state (with consistent Democratic leadership), and in a particularly liberal/progressive city or town within that state (certain college towns, like Berkeley or Madison WI, would fit that bill) would probably be pretty comfortable for most atheists.

On the other hand, living in a small town or rural area in a deep Red state, especially in the old South, would be a lot less welcoming.

Brit atheist here; I have almost no contact with any kind of religion.

The two exceptions are: Jehovah’s witnesses came to my door once – I answered the door with shaving foam on my face, so that was a quick conversation.
And the various churches in our town centres – which is a positive because they are wonderful buildings.

Now, there are those for example advocating against abortion on religious grounds…I don’t see that as a negative against atheists though, I don’t want to suppress other views.

Australia seems to be pretty safe for Atheists, in the 2021 census 38.9% of the population identified as non-religious, it’s quite rare to hear anyone talking about religion in social situations, I can’t remember the last time anyone asked me about my beliefs, I’ve never heard of any overt discrimination against atheists here

I live in a small city in the deep south. I’m an atheist. I haven’t had any more or less issues than when I lived in NYC, Boston, or Atlanta. And, personally, I’d rather live next door to a quiet Christian than a noisy atheist.

What’s the best place to be for an atheist?

A foxhole. Nobody expects atheists in foxholes.

Speaking as an atheist, I’ve always regarded that as restrictively overboard and a small black mark against France. In that case I consider individual rights are being trampled in the name of state conformity. The state being neutral is a necessity, but the individual should be allowed to do as they please as long as it is not excessively disruptive. Something like wearing a cross or a hijab does not qualify as excessively disruptive IMHO.

The heading for Iran is also inaccurate or at least more complicated than that. While not even remotely a bastion of religious liberty, the Iranian constitution officially recognizes four religions. The Abrahamic faiths of Islam, Christianity and Judaism + the somewhat anciently cross-fertile Zoroastrianism, all of whom are granted assigned seats in the Iranian parliament. Non-Muslims are absolutely discriminated against in a variety of ways, especially if you are one of the non-accepted faiths like Baha’i who have been heavily persecuted. But actually being “expected” to be Muslim is usually not one of them (though the Baha’i, regarded as apostates by Khomeini, might well quibble with my pedantry).