Our Muslim friends (at least, those who have done the slightest bit of investigation) will acknowledge that there were variants among the earliest codices of the Qur'an. However, they will insist that these variants were nothing but dialectical differences, and that the perfect preservation of the Qur'an is therefore not in question. Is this the case? Let's consider a variant in Surah 33.
Surah 33:6, in the ZSE (Zaid Standard Edition of the Qur'an), reads as follows:
The Prophet is closer
To the Believers than
Their own selves,
And his wives are
Their mothers. Blood-relations
Among each other have
Closer personal ties,
In the Decree of Allah,
Than (the Brotherhood of)
Believers and Muhajirs:
Nevertheless do ye
What is just to your
Closest friends: such is
The writing of the Decree
(Of Allah).
In his popular translation of the Qur'an, Abdullah Yusuf Ali adds the following note.
In spiritual relationships the Prophet is entitled to more respect and consideration than blood-relations. The Believers should follow him rather than their fathers or mothers or brothers, where there is conflict of duties. He is even nearer--closer to our real interests--than our own selves. In some Qira'ahs, like that of Ubayy ibn Ka'ab, occur also the words "and he is a father of them", which imply his spiritual relationship and connection with the words "and his wives are their mothers". Thus his spiritual fatherhood would be contrasted pointedly with the repudiation of the vulgar superstition of calling any one like Zayd ibn Harthah by the appellation Zayd ibn Muhammad (33:40): such an application is really disrespectful to the Prophet.
Thus, according to Ubayy ibn Ka'b (one of Muhammad's top reciters), the Zaid Standard Edition is missing the words "and he is a father of them." Ali even notes that other Qira'ahs agreed with Ubayy's! (Ali also seems to find Ubayy's version more theologically satisfying.)
Such a difference cannot possibly be attributed to dialectical issues. The question for us is this: How many variants are required if we are to reject the astounding claim that the Qur'an has been miraculously and perfectly preserved? I'd say one (though, as we've seen, there's certainly no shortage of textual difficulties for Muslims).