1)    The rapprochement of Ge’ulah to the Amidah is more important than praying with a quorum, and it follows that a person who arrived in the synagogue in the morning and finds the congregation already in the middle of the Amidah, should not omit the recital of the Shema and its affiliated blessings in order to pray with the congregation. Instead, he should first read the Shema with its blessings and then pray. (Shulchan Aruch and Mishne Berurah 111)

2)    However, in the evening service this law does not apply. Instead, it is better to pray with the congregation and afterwards recite the Shema with its affiliated blessings. (ibid)