A day on which you have not yet said Mass,with the unfortunate circumstance that you cannot offer the Traditional Latin Mass (TLM), and there are other priests with you in the same situation. For the New Mass was designed to be said with others, while the Traditional Mass largely disregards them (except the server and minister[s]).
Having to choose between concelebration and the New Mass in private, concelebration always wins (especially now in this post Benedictine Church when most priests are much more attentive than ever [since 1970] to the rubrics [a small marvel in itself]).
Contrariwise, if there's a choice between a private TLM and a concelebrated New Mass, the TLM wins every time. Because, all things being the same, when you can choose between the old and the new, you choose the old, of course! The old is better!
N.B. Priests may always simply attend Mass, with the proper vesture, in choir, i.e. a priest can attend a Mass as priest! So that this is a very reverent solution to the concelebration problem. The non-concelebrating priests may attend the community Mass in choir. It's OK! God does not mind (even if there is almost wholesale ignorance of this option among the "liturgists"). By the way, the priest is the authoritative liturgist [always under the direction of the liturgical books as approved by the Pope], ex officio! By virtue of his ordination every priest is a liturgical expert owing no allegiance to any non cleric on matters liturgical. He trumps the "liturgical committee", though he should be careful how he does that.
Every priest should follow his well formed sacramental/liturgical conscience!