I think he wore 8 the most
https://en.wikipedia.org/wiki/George_BestBest played at United when shirt numbers were assigned to positions, and not the player. When Best played at right wing, as he famously did during the later stages of the 1966 and 1968 European Cups, he donned the number 7. As a left winger, where he played exclusively in his debut season and nearly all of the 1971–72 campaign, he wore the number 11. Best wore the number 8 shirt at inside right on occasion throughout the 1960s, but for more than half of his matches during 1970–71. He was playing at inside left (wearing the number 10) in 1972 when he famously walked out on United the first time but was back in the number 11 for the autumn of 1973 before leaving for good. Best even wore the number 9 jersey once for United, with Bobby Charlton injured, on 22 March 1969 at Old Trafford, scoring the only goal in a 1–0 win over Sheffield Wednesday.[60] In total Best made 470 appearances for Manchester United in all competitions from 1963 to 1974, and scored 179 goals. Over the next decade he went into an increasingly rapid decline, drifting between several clubs, including spells in South Africa, the Republic of Ireland, the United States, Scotland, and Australia.[61]Best played at United when shirt numbers were assigned to positions, and not the player. When Best played at right wing, as he famously did during the later stages of the 1966 and 1968 European Cups, he donned the number 7. As a left winger, where he played exclusively in his debut season and nearly all of the 1971–72 campaign, he wore the number 11. Best wore the number 8 shirt at inside right on occasion throughout the 1960s, but for more than half of his matches during 1970–71. He was playing at inside left (wearing the number 10) in 1972 when he famously walked out on United the first time but was back in the number 11 for the autumn of 1973 before leaving for good. Best even wore the number 9 jersey once for United, with Bobby Charlton injured, on 22 March 1969 at Old Trafford, scoring the only goal in a 1–0 win over Sheffield Wednesday.[60] In total Best made 470 appearances for Manchester United in all competitions from 1963 to 1974, and scored 179 goals. Over the next decade he went into an increasingly rapid decline, drifting between several clubs, including spells in South Africa, the Republic of Ireland, the United States, Scotland, and Australia.[61]
https://www.transfermarkt.co.uk/george-best/rueckennummern/spieler/174986