I used to think that the bottom 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. (Using translation from Aḥmad 737)   

أَنَّ بَاطِنَ الْقَدَمَيْنِ أَحَقُّ بِالْمَسْحِ حَتَّى «رَأَيْتُ رَسُولَ اللهِ ﷺ يَمْسَحُ ظَاهِرَهُمَا»  

[Machine] And he said, "If I hadn't seen the Messenger of Allah, ﷺ , washing the backs of his feet, I would have thought their bellies were more deserving."  

وَقَالَ «لَوْلَا أَنِّي رَأَيْتُ رَسُولَ اللهِ ﷺ يَغْسِلُ ظُهُورَ قَدَمَيْهِ لَظَنَنْتُ أَنَّ بُطُونَهُمَا أَحَقُّ»