There is no way for 'you' to tell. The believer in God can tell. Because the 'Spirit' of God is active in him. If one wants to follow the spirit behind islam, by all means, follow him. Become a muslim. If you want to follow the spirit behind buddhism, then by all means follow him. Become a buddhist.
In other words, because you cannot tell, shows that you were never a Christian. Because,... the Christian can tell and knows.
Follow who you like, or be happy in your atheism. But do not think just because you and others don't know the truth, that the Christian doesn't know the Truth. He does.
Quantrill