Which is better and more deserving of constancy: seeking forgiveness (Istighfar), or sending blessings upon the Prophet (peace and blessings be upon him), or dedicating a specific time to each of them in order to obtain the reward of both forms of remembrance?

It is best to combine invoking blessings upon the Prophet, peace and blessings be upon him, with supplication (dua). However, if one limits themselves to invoking blessings upon the Prophet, peace and blessings be upon him, it is hoped that they will attain goodness, have their sins forgiven, and their worries be taken care of. Imam At-Tirmidhi narrated from Ubayy ibn Ka'b, may Allah be pleased with him, that he said to the Prophet, peace and blessings be upon him: "Should I dedicate all my prayers to you?" He replied: "Then your worries will be taken care of and your sins will be forgiven." Sheikh Al-Islam Ibn Taymiyyah explained that "my prayers" here means "my supplications," i.e., dedicating the time for supplication to invoking blessings upon the Prophet, peace and blessings be upon him.