A person who finds it difficult to have kavanah when praying in a congregation, but succeeds in retaining the basic kavanah with which he fulfills his obligation, must pray in a minyan, even if he concentrates better while praying individually. As long as he has kavanah for the first berachah of Shemoneh Esrei, he must pray in a minyan (Igrot Moshe, Orach Chaim, part 3, 7). Moreover, in the long-term, consistent praying with a congregation usually strengthens one’s kavanah and connection to matters of sanctity.
A talmid chacham (Torah scholar) whose learning is his profession, must try to pray in a minyan, even though the walk to synagogue to pray in a minyan causes him to lose time from his learning. Though, in principle, he is allowed to pray individually, he must be scrupulous to pray in a congregation, so that people will not learn from him to belittle the matter of communal prayer. Only on rare occasions, when he is in the middle of an important subject of study and the walk to a minyan will greatly disturb his learning, is he permitted to be lenient and pray individually (based on the Rama 90:18).
With regard to one who teaches Torah to others and is unable to both pray in a minyan as well as teach his class, it is better that he pray individually and not cancel his class, for the communal learning of Torah overrides praying in a minyan (Mishnah Berurah 90:56).
It is preferable to pray with a congregation rather than take part in the meal of a brit milah (Kaf HaChaim 90:67). However, in a case in which the host of the seudah (meal) is likely to be insulted if a particular person does not attend, it is better that he pray individually and participate in the seudat mitzvah in order to prevent a rift.
When a person has two options: to pray individually “vatikin” at sunrise (netz) or to pray in a minyan later, most poskim maintain that it is preferable to pray in a minyan (see also further in this book 11:9).