Which is better and carries a greater reward: praying Fajr in congregation and remaining seated until sunrise then sleeping, or praying Fajr and remaining seated for half an hour to recite remembrances then sleeping and waking up early for Duha prayer?

Remaining in the prayer area until sunrise is a confirmed Sunnah of the Prophet, and its reward is equivalent to the reward of a complete and perfect Hajj and 'Umrah. Therefore, engage in this great Sunnah due to its virtue and because it is the worship of the [appropriate] time. If you wake up before noon, pray Duha and whatever else is easy for you to pray, for prayer is the best of deeds.