Which is the best? IV, obviously, because it’s the most manly.
Most popular? III, hands down.

I would suggest Credo I as it is the authentic tone. Followed by Credo IV. Too many sing the modern Credo III all the time.

We sing Credo I for Feasts and Eastertide, II for Lent and Advent, IV for after Epiphany and Pentecost, and VI occasionally. EF of course.

The rest are a riff on it or are much later independent compositions, particularly III and IV which are mensuralist (as the French would perhaps say "à la base"; I've never found a good English equivalent; "originally" is the idea, but not quite the same…), but err, few people perform them this way, and there is a certain beauty to the Solesmes versions of this, the simple Salve, etc.

I vote for Credo I.
It is the only one ever used at Sarum.

Our current schema:

Credo I - Major Seasons/Solemnities (Christmastide/Eastertide)
Credo II - Advent
Credo III - Sundays of the Year
Credo IV - Septuagesima through Lent.

Our Credo cycle (always congregational):

Green Sundays - IV
Advent - I
Christmas - III
Lent - I
Easter - III or IV
Feast Days ad libitum (can be a great way to keep I & III fresh through the weeks of IV)

Sure! It partly grows out of what I inherited. For Green Sundays, my predecessor had taught Credo IV very well and used it regularly, and I had *no* issue with it being the regular Credo as (1) I already preferred it to the other settings of the Credo, and (2) the people sang it extremely well.

Bear in mind, that is our *default* setting, but over the long stretches I will switch it up from time to time with one of the other two, to keep them fresh and to prevent too much of a 1-to-1 association of Credo with either a penitential or festival season.

Credo I during penitential seasons strikes me as appropriate because it is in many ways the most austere, and also because I have always viewed penitential seasons as a time when the Church invites us both on the level of our spiritual lives, and in our liturgical praxis, to go back to basics and focus on what is most essential -- so we use those weeks to ensure that the "authentic tone" of the Credo is well-known by the faithful, 'going back to basics' as it were.

Using it on the occasional feast day and Green Sunday helps make sure it doesn't come to carry too penitential of a connotation.

Credo III fits well into the Christmas season because the primary chant Glorias we will hear during that season here are IX and VIII, and it lives in a similar sonority. It also pairs well with a lot of polyphony and later music, being more major-key, and less modal, and often invites polyphonic interpolation of, e.g., the Et incarnatus est on feast days of Our Lady, so it fits well into Eastertide, which tends to have more polyphonic content.

How do you introduce such things (an unknown Credo or a new Mass setting) to the parish? @NihilNominis you say your predecessor "had taught Credo IV"? Does that happen before or after mass? I find it difficult to find an occasion where a) you have the parish gathered and b) you do not distract from the mass.

Yes. We introduced Mass IV by doing it for a few Masses in October-November. They haven’t quite gotten it but they at least know the Kyrie well. I put out booklets for those Masses.

I’d do the same with IX. I love Mass XI, it’s my favorite other than IV, but I would sacrifice it to teach a new Mass.

Now YMMV. Our people are enthusiastic.

I don't find Credo VII to be simple; we always found it tough because the musical accents are in the wrong place with respect to the textual accent in a way that is not usually the case for formulaic, syllabic chant.

I only know of the Credo VII linked above. Where would I be able to find alternate versions? You've piqued my curiosity.

Some of the links in this thread are broken, but the information on Credo VII is there.
https://forum.musicasacra.com/forum/discussion/2690/credo-vii-not-a-typo/p1

Thanks! The Credos fascinate me, and it's good to have another one to throw on the pile. I've heard there are hundreds of cantus fractus Credos in the Giunta Gradual and other books ~ 13-17th century. I haven't been able to find any pdfs of such books, but if anyone knows of any, please send them my way! I already have the Spanish Credos, but those are great to consider as well.

Credo II is fairly similar to Credo I, and shares a lot of melodic material. Two pieces which have the same words, and much similar melodic material, but some differences, are more likely be be sung incorrectly, especially by those who are singing primarily from memory rather than comprehension of a score. The shared material between two such pieces may cause false memory cues, which then could lead to mistakes in the places where the melodies do differ. This may have been the reason for Credo II's exclusion from the SSPX hymnal, but I cannot say for sure.

We sing I on Feasts and II in Advent and Lent. The Congregation can cope with this...

I’ve never heard II in the wild. Maybe the SSPX used it more in some places. But yes, not including II would serve to exclude it for whatever reason.

I don’t think that VI or VII are more popular. They’re all pretty much relegated to novelties at most for most of us. I, III, and IV dominate. And understandably.