1. Ali: Transcended the sport, dominated the best of three generations during the best era of heavyweights ever, participated in numerous GLOBAL events and delivered in every single instance. Overcame significant odds to defeat two of the most intimidating boxers in history- Liston and Foreman.
2. Joe Louis: Overcame the color barrier and won arguably the most important fight in history (vs. the German Schmeling) when the country needed him most. Most title defenses in history, in any weight. One of the most fearsome punchers in the history of the sport. Comes second to Ali on my list due to quality of opposition and knockout loss during his prime.
3. Larry Holmes: Never unified the titles, but was the best big man for years, making 20 successful defenses and coming within one fight of tying Marciano's 49-0 record. Great boxer-puncher who beat decent competition, but never faced a prime, elite level fighter. I can see a solid case for ranking Larry lower, but I just think the guy was a phenomenal boxer in his day.
4. Evander Holyfield: Second best resume'/quality of opposition on this list, facing all of the big names during his time (Foreman, Tyson, Bowe, Lewis, Moorer...etc.). Was the second fighter to win the lineal championship 3 times (Ali was the first), and won titles on (multiple) additional occasions. Evander's consistency and habit of fighting down to his level of competition hurts him on my list, but his heart, skill, work ethic, and willingness to fight the best get big points on my list.
5. George Foreman: Two time lineal champ, spanning decades between reigns. One of the most fearsome fighters during his prime, and then transformed into one of the most loveable during his comeback. George destroyed fellow ATG Joe Frazier during his prime, and blew out HOFer Ken Norton in impressive fashion. His knockout of Michael Moorer made him the oldest champ ever (until BHOP), and his record as oldest heavyweight champ still stands today. George's limitations against boxers and his losses to Ali and Young during his prime lower his standing on my list.
6. Joe Frazier: Unified the title and won the Fight of the Century vs. the Greatest Heavyweight ever. Beat solid opposition and was a feared champion (thanks to his murderous left hook), until running into his perfect foil in George Foreman. Blowout losses to Foreman hurt him on my list.
7. Rocky Marciano: Retired with a 49-0 record, but benefitted greatly by coming along during one of the weakest heavyweight eras in history. Marciano was a hard puncher with unbelievable work ethic/stamina and one of the biggest hearts the sport has ever seen. The Rock's weak level of competition hurts him on my list, with his consistency/100% win percentage pushing him into my top 10.
8. Lennox Lewis: Great champ who fought and beat every man he ever shared the ring with. Beat solid competition during his prime (Holy, Ruddock, Golota, Morrison, Mercer...etc.). Knockout losses to journeymen Oliver McCall and Hasim Rahman kill his placement on my list.
9. Wladimir Klitschko: Fragile mentality and constitution, but dominated the division for many years. Very skilled for a big man, very intelligent in the ring, and a physically imposing/intimidating heavyweight. Losses to Byrd, Saunders, Brewster, and Fury make Wlad's top ten placement difficult to justify, but his consistency and the fact that he cleaned the division out wins out for me in the end.
10. Mike Tyson: Youngest heavyweight champ ever. Unified the titles and forced the fat, lazy heavyweights to take the sport seriously and get in shape. One of the most intimidating fighters ever, with one of the biggest punches in addition to lightning reflexes and speed. Mental stability and toughness hurt Tyson's ranking on my list, as do his stoppage losses vs. Douglas and Evander. Feel that like Holmes, Tyson was fortunate to fight during a weak era of heavyweights and showed his limitations when he stepped in with solid fighters who weren't intimidated and were committed to winning.