IMO Holy God We Praise Thy Name belongs at top of this list for non-seasonal hymn repertoire. I can't speak to the British Isles, but at least for the USA, it still seems to be the most universally and vigorously engaged of general hymns in the vernacular. Which is meet and just. Any pastor and/or music director who is tempted to let it drop out of regular use should . . . reconsider. If the Parousia were to occur soon, what hymn would most active American Catholics be likely to sing well together en masse with no instrumental support?

To repeat something I've mentioned at least once before on these boards:
A least a couple of decades ago, I heard a wonderful (but quite likely apocryphal, as I've never found a proper source for it) story about Grosser Gott: that, during some propaganda rally in World War II in Germany (the version I heard included Goebbels as haranguer-in-chief for the occasion), someone in the crowd started singing Grosser Gott, which was gradually taken up by the crowd and drowned out the haranguer. The very thought of this pleases me - the very reason I am a bit skeptical about what ultimately is or is not true about it. Apropos of this, here's a glorious mess of Grosser Gott in the immense acoustic (that vault is 43m / 141' high) of Cologne's cathedral:

https://www.youtube.com/watch?v=cJ2DhRItaoA

So, as a musician, I love when hymns are sung with fine musicianship. That said, the cradle Catholic in me at the same time appreciates that kind of glorious immense mess, which has a sincere, heartfelt integrity of own that is sublime in a different yet coexisting way from musical perfection.

"Lift High the Cross" on Holy Thursday.
"O Come All Ye Faithful" on Christmas Day.
"Immaculate Mary" whenever it is sung.

For years, I have been looking for an opportunity to record my observation of just such enthusiastic congregational singing. My wife and I were married in 1965, and that summer, we were hiking in the Tetons with another couple. We went to the Sunday Mass in Jackson Hole, WY, and I was impressed by the vigorous full-house congregational singing. (probably the 4-hymn format) Subsequently, I realized that the local parish had very few resident Catholics. It's safe to say that those who go to Mass while on vacation would be the most likely to participate in the service. Laudetur Deus!

CS

Brilliant! The condensed detail in your second offering is priceless!

As for the first: I might well imagine that Rod has a tendency to flatness while Susan has a tendency towards sharpness - of which neither is fully aware. (Imagination from actual experience of a quartet of singer-musicians at a now-closed Catholic church outside the western edge of Rochester NY.)

Our parish list:

Holy Holy Holy
Sweet Sacrament
Sacrament Most Holy
The Summons
Christ Be Our Light
Salve Regina
Immaculate Mary
O Come Divine Messiah

Anything sung at daily Mass, unaccompanied, led by one of the church ladies, at least a 4th lower than what is written in the hymnal, sort of in time, mostly in tune. I do appreciate their enthusiasm. As a soprano, it pains my heart to sing some of these that low.

The very first hymn I learned when I started weekly attendance at Mass circa 1965 was Holy Holy Holy. My father took the boys to the earliest Sunday morning Mass; my mother took the girls to a later Mass; six kids - divide et impera was their management rule for this. My father grew up in German national parish that *sang*; my mother sang (and a better voice, though very low in her register- a female tenor, essentially), but her Irish parish generally left singing at Mass to the parochial school choir. So my father always sang at Mass - and not shyly - and modeled that for me. He was unusual among men of the period and place for so doing, and I am deeply grateful for his example.

At our Traditional Latin Mass, any Church Militant type hymns gets sung with great gusto, especially To Jesus Christ, Our Sovereign King and Faith of Our Fathers (not to be confused with the liberal faith of our sisters and mothers aberration found in CBW III). They also sing the Ambrosian Gloria, Mass VIII, the Litany of the Saints with gusto as well.

Our English Mass just doesn’t sing hymns for the most part. There’s a few of us who sing the good traditional hymns with gusto, but I was sorely let down by the congregation on the Feast of Christ the King with the sad state of To Jesus Christ, Our Sovereign King. I think there may be some confusion about singing at Mass and that it’s a choir performance. They always tend to clap for the choir after Mass.

Many of the traditional Advent carols are popular—“O Come, O Come, Emmanuel” probably tops the list, followed by “O Come, Divine Messiah,” and “People, Look East.”

Any of the mainstream Christmas carols are also a hit.

In addition to the “ordinary” hymns already mentioned, our folks really sing “Come, Christians, Join to Sing.”

At Easter, we do a really oldie but goodie with Fr. Rossini’s “Christ is Risen from the Dead.” They really sing that.

To Jesus Christ Our Sovereign King, and O God Almighty Father were very well known out the Archdiocese of Oregon, and always sung with gusto, back in the 70s. Let All Mortal Flesh was also well known. I was too young to know if the Archdiocese was recommending hymns, but the two approved hymnals were the People's Hymnal, 1955 edition, and Our Parish Prays and Sings (especially if there was a school--many of the rural parishes and missions did not have schools). One other hymn that was used frequently, but was not sung very well if the tempo was too slow, Praise the Lord of Heaven, UNE VAINE CRAINTE. I once, when college aged, stumbled on the end of a reunion service in one of the (many) German heritage parishes. The hymn begin sung was Grosser Gott, and the singing was thunderous. I was in the narthex, and after the first verse, the stampede for the doors began, and I had to scurry away lest I be trampled.

As I Kneel Before You (you will all HATE this one, I am sure!!!)

It came over to me some years ago on a local parish wedding list, attached to a claim (which I presume is false) that it was inspired by Medjugorje. I have a lot of tolerance for treacle, but this is awful on a level that requires effort to be that bad.