My actual reason to leave islam were both hadis and quran.
when I started coming across crazy stuff in books of ahadees(bukhari etc) like slave sex and stories of aisha as a child. I started to realize that the muslims who reject ahadis are actually trying to save islam.
So i knew that okay quran will have to be the last thing standing afterall it is claimed to be the word of god so when everything has failed quran still needs to be looked into......
and when I found out that quran does not stand upto the claim that it has never been changed and that there are differences in even phrases when we see ancient manuscripts like topkapi and samarkand...... its credibility seriously deteriorated and as it is the basis of islam the whole religion fell apart......
and then every little criticism about religion started looking so big and real.......... and very often i think that if it all started with one guy going into a cave(muhammad) or upto a mountain (moses) and then coming down and telling he has been contacted by god in isolation........in a time when people obviously had almost no scientific understanding of nature and were extremely supersticious......... then they(prophets) were obviously lying and were just playing by the trends then......
even his companions had never seen anything happening they also just took it on his words just like we have to do today.......... an obvious lie.........if god was really expecting everyone to be so dumb to just take it on words then he clearly was underestimating his creation