The most worthy condition which must be fulfilled is that which makes sexual intercourse lawful. In the narration transmitted by Ibn Muthanna (instead of the word" condition" ) it is" conditions".  

قَالَ رَسُولُ اللَّهِ ﷺ إِنَّ أَحَقَّ الشَّرْطِ أَنْ يُوفَى بِهِ مَا اسْتَحْلَلْتُمْ بِهِ الْفُرُوجَ هَذَا لَفْظُ حَدِيثِ أَبِي بَكْرٍ وَابْنِ الْمُثَنَّى غَيْرَ أَنَّ ابْنَ الْمُثَنَّى قَالَ الشُّرُوطِ