The month most liked by the Messenger of Allah ﷺ for fasting was Sha'ban. He then joined it with Ramadan. (Using translation from Abū Dāʾūd 2431)
أَنَّهُ سَمِعَ عَائِشَةَ تَقُولُ «كَانَ أَحَبَّ الشُّهُورِ إِلَى رَسُولِ اللَّهِ ﷺ أَنْ يَصُومَهُ شَعْبَانُ ثُمَّ يَصِلُهُ بِرَمَضَانَ»