My condolences that you always use Missa de Angelis outside of Advent and Lent. It's not an evil Mass setting, and I don't mean to suggest that it is. On the other hand, pizza with ice cream is fun once in a while, but not every day, at every meal!

This is difficult. My favourite? It depends on what day it is.
My two unfavourites are easier: Orbis factor and de Angelis (not to mention XVIII most of all).
Cum jubilo and Pater cuncta come to mind as especially nice. But, they are all especially nice, except the unfavourites mentioned above. I am puzzled that the mass for Eastertide, Lux et origo, is one of the simplest. One would rather think that the mass for Eastertide would be somewhat melodically extravagant. Not so! Too, a number of the ad libitum kyries are really fantastic. They should be used more often.

If you want to change things a little, use Missa De Angelis for Easter and Christmas, Orbis Factor for Ordinary Sundays and Mass XVII for Lent and Advent.

Also, I would use Credo III for Easter and Christmas, and Credo I for most of the rest of the liturgical year.

The question is whether or not you want congregations to sing the chant ordinaries. You would have make Kyriales available in the pews and on the hymn board put up "Mass" and a number.

Mass V, Missa Magnae Dei potentiae is my favorite right now at this moment, but Mass VI, Missa Rex Genitor, and Mass VII, Missa Rex Splendens are also huge favorites and Mass XIV and Mass II are mystical and enchanting. I really can't say which one is my absolute favorite---that would be like asking what my favorite flower, or my favorite ice cream is since I've never seen a flower I didn't love, or ice cream that I didn't like, though if I had to have an absolute favorite flower it would be a violet, and plain homemade vanilla custard ice cream beats all else in my estimation.

Thanks for asking; that was fun. : )

I would love to say I had a favorite, but I can not. I do not know any but Missa de Angelis. It is very unfortunate, I am required to sing only Masses in the pew missal of choice at the Church where I play and they only have the "Chant Mass" setting which is a combination of a few ordinaries. So I guess my favorite would be Missa de Angelis because I know it and can play it from time to time.

Um, how does one say 'The Saucy Maid' in Latin?
I'm sure it would be a very interesting trope!
Mass XII, Missa........

I'm not sure I understand the antipathy towards Mass VIII. Strangely, I somewhat disliked it until we sang it for four Masses a weekend for the entire season of Easter and Trinity and Corpus Christi (at the pastor's direction). Then what I discovered was that I didn't dislike Mass VIII; rather, I dislike the existing accompaniments -- all of them. There is something cheap about most of them, and it is a cheapness which I previously and incorrectly attached to the chant itself. Either sing it a cappella, or come up with an innovative accompaniment. We did a combination of the two.

So I will be the outcast who rather loves Mass VIII, repetition having increased my appreciation.

Yet if I had to pick a favorite, it would be Mass IX.

I must admit a certain psychological attachment to the Sanctus of that Mass; my first "aha" moment of recognizing a Gregorian chant theme in secular music was when the familiar melody (which I had heard in my church growing up) of that Sanctus rose up gloriously out of the Catacombs in Respighi's Pines. I first heard it as a high school freshman, when I played the organ part for the county youth orchestra's performance of that work. It took several years before I realized why that melody was so familiar.

https://m.youtube.com/watch?v=9KNGEVuBqMQ

Some people disfavor Mass VIII due to its late composition (16th century: why, it's so tonal, not modal!). Also, it's overused.

I suspect that some people favor it to the point of overuse because of its tonality; and due to its nickname, combined with the impulse to express a little appreciation for the Holy Angels. If it were called Missa de apostolis, for example, it might not get nearly the fan base it has.

puella petulans

I've always liked XI, "Orbis factor." To me, and for lack of better terms at this early hour of the morning, there's just an ultra-mystical / mysterious / haunting quality about it that I love.

I agree with Dr. Mahrt: Mass IV! It was the ordinary for my nuptial Mass...6 years ago yesterday! I can never decide how good a "congregational Mass" it is. I think Orbis Factor (and maybe Mass XII?) the easiest for modern ears to hear and respond to; Mass VIII is more familiar, but is much more florid.

Kyrie Rex Splendens, etc., and Kyrie stelliferi Conditor, etc., without a doubt.

I still don't quite understand if the centuries indicated in the Solesmes books refer to the oldest or merely the principal sources.

For a history of Missa de Angelis try Caecilia vol 60 no12, Dec 1933 http://media.musicasacra.com/publications/caecilia/caecilia_v60n12_1933_12.pdf.

Okay, maybe I'm just crazy, but is Kyrie VII a subtle reference to Christ as the Alpha and Omega? I was listening to it without consulting the score, and I was so sure it was mode I, but when I looked, it is indeed mode VIII. Throughout, it carries a tonal quality and structure common to mode I, but then finishes on Sol, making it mode VIII. Again, Alpha and Omega?

Haha, Ralph, I didn't see this till now. Last Halloween I decided to dress up as my favorite writer and intercessor, Chesterton, and walked around all night as if I was an old, fat Englishman. It was great fun.

Mass IX is a favorite. I second what Salieri said about Mass XIII Stelliferi Conditor Orbis.