Ali, he fought when boxing was way more aggressive and he was still one of (if not the best) fighters out there and he is still known as the best

Just like your previous questions (a few which I didn't get to answer), solely based on resumes, what I do to determine whose was more impressive, I look at their records, how many world champions they've defeated, how many world champions they've lost to, what their record in world title fights was and who won more world titles and had more defenses. Then, I come up with my conclusion.

Muhammad Ali:
~ Retired with a record of 56-5, 37 KOs.
~ Defeated the following world champions; Archie Moore (KO4), Sonny Liston (KO7, KO1), Floyd Patterson (KO12, KO7), Ernie Terrell (W15), Jimmy Ellis (KO12), Bob Foster (KO8), Ken Norton (W12, W15), Joe Frazier (W12, KO14), George Foreman (KO8), Leon Spinks (W15).
~ Lost to the following world champions; Joe Frazier (L15), Ken Norton (L12), Leon Spinks (L15), Larry Holmes (KO BY 10), Trevor Berbick (L10).
~ Had a record of 22-3 in world title bouts.
~ Won the following world titles; World heavyweight (7 successful defenses), WBA heavyweight (1 successful defense), WBA heavyweight (10 successful defenses), WBC heavyweight (10 successful defenses), WBA heavyweight (never defended).

Evander Holyfield:
~ Currently has a record of 43-10-2, 28 KOs.
~ Has defeated the following world champions; Tyrone Booze (W8), Dwight Muhammad Qawi (W15, KO4), Ricky Parkey (KO3), Ossie Ocasio (KO11), Carlos De Leon (KO8), Pinklon Thomas (KO7), Michael Dokes (KO10), James Douglas (KO3), George Foreman (W12), Larry Holmes (W12), Riddick Bowe (W12), Ray Mercer (W10), Bobby Czyz (KO5), Mike Tyson (KO11, W BY DQ3), Michael Moorer (KO8), John Ruiz (W12), Hasim Rahman (W BY TD8). Also drew with the following world champions; Lennox Lewis (D12), John Ruiz (D12).
~ Has lost to the following world champions; Riddick Bowe (L12, KO BY 8), Michael Moorer (L12), Lennox Lewis (L12), John Ruiz (L12), Chris Byrd (L12), James Toney (KO BY 9), Sultan Ibragimov (L12), Nicolay Valuev (L12).
~ Has a record of 16-7-2 in world title fights.
~ Won the following world titles; WBA cruiserweight (5 successful defenses), IBF cruiserweight (3 successful defenses), WBC cruiserweight (never defended), WBA heavyweight (3 successful defenses), WBC heavyweight (3 successful defenses), IBF heavyweight (3 successful defenses), WBA heavyweight (lost it in first defense), IBF heavyweight (lost it in first defense), WBA heavyweight (4 successful defenses), IBF heavyweight (2 successful defenses), WBA heavyweight (lost it in first defense).

To conclude, this one looks tough to choose on the surface but when you really delve deep, I think that you have to go with Muhammad Ali. Ali had a better win-loss record, Holyfield beat more world champions but you have to remember that Holyfield fought (or is fighting) in an era with 4 world titles in each weight division and he fought in 2 divisions whereas Ali fought in 1 division with 1 world champion for a good portion of his career and then when he made his return, there were only 2 world titles per division. If there were 4 world titles when Ali was fighting, he could quite possibly have defeated more world champions than Holyfield, and when you look at the actual names that Ali beat, they are far superior to the ones that Holyfield beat- Ali has more hall of famers even though he only beat 10 world champs compared to 17 for Holyfield. Ali also had a MUCH better record in world title fights and had FAR more title defenses than Holyfield, who lost more than a quarter of the time that he fought in a title fight whereas Ali only lost 3 times in 25 title fights. Even though Holyfield defeated more champions and won more titles, Ali's resume is superior due to the actual champions that he defeated (which is the best group of heavyweights in history) and even many of the contenders that he defeated were superior to the champs that Holyfield defeated because if there were 4 titles back then, some of them WOULD have been champs, and due to his superior longevity as a champion (i.e. having more success in title fights when it mattered).

Ali, because Frazier, Liston, Holmes, Foreman and arguably a couple of others in his resume are all time greats, whereas Holyfield although he fought the top men around in his time, other than Foreman and Tyson who were both past their primes, he didn't beat any all time greats. No disrespect to him whatsoever, like I say he beat the best available and was a great champion but Ali has the better resume.

Both men have very impressive resumes. You picked well because, all things considered, I don't think any other heavyweight champion has a better resume than these two champions.

Two things tip it in ALI's favor. One: They have one common opponent, George Forman. Forman was well past his prime when Holyfield beat him. ALI Took Forman out of his prime. . . Two: ALI beat the best heavyweight champions in history while they were in, or closer to, their primes than he was to his. He was the central part of Heavyweight history's Golden Era after his prime was unjustly taken from him.