In our case, we simply cycle through all seven Credo settings (including the one from the 1927 Graduale) through the year so there is essentially even distribution across the season. I typically use Credo VI for Lent because I find it penitential in character, but clearly all have a different perspective as you can see from Tomjaw's response above.

I don't find it useful to match it with a given ordinary setting.

For polyphonic Masses, I typically learn the Credo after we've got the full setting - sometimes a year or three later. Once learned, we schedule that Credo anytime we use that part-setting. Similarly with extraordinary Ordinary settings (du Mont, St. Hildegard, etc.). We learn those a year or three later, and use one of the seven settings that we feel relatively comfortable with otherwise.

Since repetition is a useful pedagogical tool, I use Excel to auto-count my usages of each Credo, each Ordinary setting, each motet, each hymn to make sure I avoid (as best I can) single use, over-use, or under-use, when building out my schedule at the beginning of a given season. For Credo usage this season:
I 7
II 7
III 8
IV 7
V 6
VI 7
VII 6

For most of the Credo settings, I try regular recurrent patterns so that the choir has comfort level, to divide into two recurrences. So Credo I, I might schedule 4x in a row, and then later in the year 3x in a row. That allows review of each setting and establishing a comfort level. Credo VI is the exception - since I typically use that as a penitential Credo, it is for some combination of Septuagesima-tide and Lent, although I have sometimes split its use between Advent and Lent.

In answer to your question, there is no rule that specifies which setting to use when. Each director comes up with their own approach. I knew someone who always used IV for Marian feasts. Lots of places only use I and III (which I find unfortunate, since each setting has a unique flavor).

As mentioned above, we use all Credo settings each year. For the Masses and ad-lib chants in the Kyriale, we use all settings across a 3 year schedule. I've found that doing this dramatically improves the choir's ability to sing chant well - they see a lot of different thematic devices and don't take anything for granted.

EDIT: I should add that as part of whole premise of incorporating this pedagogically, we also switch the order of alternation every 3 years... so, in the Kyrie, Gloria, Credo, while the men typically begin following the intonation alternating against the ladies, next season, the ladies will begin following the intonation and alternate against the men. It is an extension of not taking things for granted, and ensuring that everyone is familiar with the entirety of the Kyriale. Mass IX and X Gloria; Kyrie 1 ad lib; Gloria 1 ad lib - four exceptions, where because of the range, ladies always start.

According to Justine Ward (for what it's worth):

Credo I. The best according to Dom Mocquereau.
Credo V. The next best.
Credo VI. The next best.
Credo III. Frankly modern but unobjectionable.
Credo IV. Not Gregorian Chant but the soprano voice stripped off a polyphonic composition.
Credo II. The worst of all. A poor, mixed up adaptation of Credo I.

I'm sad to read such a commentary about Credo IV. I've been advocating for its use because I find it so hauntingly beautiful.

This text is on the last page where the Kyriale et Credo are in the Liber.

"This Ordinary is NOT meant to be a matter of hard and fast rule : chants from one Mass may be used together with those from others, the Ferial Masses excepted. In the same way, in ordr to add greater solemnity one or more of the following may be employed." Liber Usualis 1962 pg. 78

So pretty much it's all about opinion................Unless otherwise stated.

(OF) We use an Englished Credo III on all Sundays and whenever there is a sung Mass requiring the Creed. I would prefer we use Credo I, but there's no Englished version in the St. Michael hymnal (our hymnal), and the PIPs are 99% unwilling to learn/sing a Latin Credo. At the end of the day, I'm just happy we get to sing it regularly, regardless of language and melody.

He still in Detroit?

He’s not a doctor unless I missed something.
He still plays at St. Benedict TLM Community in Windsor and the Oakland County TLM in Detroit every week as far as I know.

Haha @StimsonInRehab ^ so true. What you think about your being a doctor?

@Hugh do you have a calendar of when you use the various credos?

The other was Clear Creek Abbey, ... They would use Credo III for the days ranked as "Feast" which require a Creed - which is not very many, in the Novus Ordo Calendar ... for the Kyriale they basically follow the recommendations found in the Liber, modified to fit the Novus Ordo's ranking system.

Somebody could explain this? I always thought that Clear Creek uses the Vetus Ordo and that they just have the Feasts of the Saints on the dates they have in Novus Ordo. But how they are able to use rubrics regulating the use of Credo and feast ranking foreign to the traditional form of Roman rite?