I would highly recommended the
Jubilate Deo setting. It is very easy to sing, and is ideal for congregations who do not frequently sing chant, but is also good for experienced ones.
Kyrie
Gloria
Credo
Sanctus
Agnus Dei
These Mass parts were put forward by Pope Paul VI as
minimum repertoire of Gregorian chant for every catholic.
Here is why this is an excellent setting to use for Mass:
GIRM:
All other things being equal, Gregorian chant holds pride of place because it is proper to the Roman Liturgy.
…
Since faithful from different countries come together ever more frequently, it is fitting that they know how to sing together at least some parts of the Ordinary of the Mass in Latin, especially the Creed and the Lord’s Prayer, set to the simpler melodies
De Musica Sacra:
Steps should be taken enabling the faithful to say or to sing together in Latin those parts of the Ordinary of the Mass belonging to them