I used to think that the bottoms of the feet were more deserving of being wiped than the tops, until I saw the Messenger of Allah ﷺ wiping the top (of his feet).
أَنَّ بَاطِنَ الْقَدَمَيْنِ أَحَقُّ بِالْمَسْحِ مِنْ ظَاهِرِهِمَا حَتَّى رَأَيْتُ رَسُولَ اللهِ ﷺ يَمْسَحُ ظَاهِرَهُمَا