The month most liked by the Messenger of Allah ﷺ for fasting was Sha'ban. He then joined it with Ramadan.  

سَمِعَ عَائِشَةَ تَقُولُ كَانَ أَحَبَّ الشُّهُورِ إِلَى رَسُولِ اللَّهِ ﷺ أَنْ يَصُومَهُ شَعْبَانُ ثُمَّ يَصِلُهُ بِرَمَضَانَ