The adhan has been narrated in several versions, all of which are valid. See the explanation of that in the long answer. Therefore if the mu`adhdhin chooses one of them to recite, there is nothing wrong with that, and you can repeat after him.

If a person is reading the Quran and the Mu’adhdhin gives the call to prayer, it is better for him to stop reading and focus on following the Mu’adhdhin in obedience to the Sunnah of the Prophet.

It is disliked to sing the Adhan in the sense of elongating the words excessively without changing the meaning. If the meaning is changed, then it becomes prohibited and the Adhan is not correct in this case.

1. It is not stipulated that the Adhan should be given by any particular person. So, if a Muslim man gives the call to prayer, the communal obligation is waived from the people of that locality. 2. One of the conditions, without which the Adhan is not valid, is that the Mu'adhdhin should be a male Muslim of sound mind. 3. It is desirable that the Mu'adhdhin should have a beautiful voice, and he should be trustworthy, of good character, knowledgeable about the times of prayer, and an adult.