Why did Uthman burn all other versions of Quran and how did he choose the perfect version?

Quran was well memorised by each and every Muslim, on that time papers or leaves was getting burnt Quran was already memorised. Even Muhammad himself he did. Even if all the Quran around the world get burnt, still the Quran will be written in its original form. It won't be the second version. No Muslim can memorise the Quran when reading it and jump any single word. Muslims are instructed to memorise the Quran and not to leave or increase any word when reading. Muslims believe that to leave or to add any word in the Quran is a sin to God {Allah}. Whether you are a Sunni or Shia Muslim you have to read in the same way as the Quran received from God to Muhammad peace be to him. The same Quran is read in Malawi the same they read in Saudi Arabia, Nigeria, Israel and so on.

Uthman appointed a Committee comprising: Zaid b Thabit, Abdullah b Zubair, Saeed b Al 'Aas , and Abdur Rahman b Al Harith. This Committee was commissioned to prepare an authorized text. Copies of the Holy Quran in use in various parts of the dominions were collected and compared with the copy in the custody of Hafsa which had been compiled in the time of Abu Bakr. The Committee worked hard. All the discrepancies were reconciled, and an authorized standard edition was prepared. Uthman checked the compilation himself and finally approved it. Copies of this edition were prepared and supplied to all parts of the dominions. All previous copies in use in the various parts of the Muslim dominions were collected and burnt.

This was a measure of great importance and significance, and thereby Uthman did a great service to the cause of Islam. The books revealed to all previous prophets had been corrupted by the followers of the respective prophets. But for the measure undertaken by Uthman, the same fate would have befallen the Holy Quran. Uthman deserves the gratitude of the Muslims by this single service in preserving the Holy Quran in its original form free from any corruption. It is surprising that some of the critics of Uthman made this measure a matter of criticism against Uthman. They urged that the burning of the copies of the Holy Quran with a view to introducing a uniform text was a sacrilege. This criticism is entirely misconceived. The burning of the unauthorized texts could by no stretch of imagination be called a sacrilege. It was on the other hand a most pious act inasmuch as it united the Muslim community on an authoritative and standard text for all times.

The Burned things wasn't Quran , [Quran is the words that we read not the papers ] and Othman burned separated paper [actually in that time was tree Leafs and other like ] not a full version , and they wasn't different , some of people were writing some notes on the margin or explanations by the Prophet and like this , and Othman burned these papers to avoid confusing peoples' notes with the Quran .

Also the group that copied the final version wasn't Othman him self , but 6 persons who have to find 2 witness(at least) for every Ayah (Quran is more than 6000 Ayah)

The most important thing to know is that Lots of Arabs were memorizing the whole Quran , and Reading was a secondary way to carry Quran to others , it was been carried verbally all the time.