moving up and fighting in a new weight class for the first time in their careers and defeating a top 3 all-time great in their divison? Spinks against a Larry Holmes who had never lost Leonard against a Hagler who had not lost in over 10 years
For me it's Leonard vs Hagler based on the inactivity and the fact I think Hagler was in considerably better form than Holmes was. For example Holmes was coming off a controversial decision against a green Carl Williams that quite alot of people had him losing. Hagler was coming off destroying John Mugabi who had a 100 percent KO ratio.
It would be difficult to vote against Leonard-Hagler. For one, Leonard and Hagler (at that time) were both (Leonard clearly was, but you could argue Hagler was as well) bigger mainstream sports stars than either Holmes or Michael Spinks were when they fought. Second, Leonard-Hagler was a much bigger event (closed circuit TV) ... Holmes and Spinks was on regular HBO. Third, as was just mentioned, Hagler was coming off the exciting win over Mugabi in a great war. Holmes was sort of on auto-pilot. Larry was champ for so long and won so much, people sort of lost touch with his defenses at that point. Hagler was still grabbing headlines with his defenses. But all that said ... I think Spinks' performance was much more impressive than Leonard's. Nobody really thought Holmes won. People still argue strongly today that Hagler deserved to win. And also no light heavyweight champion had won the heavyweight title before. Michael was the first to do it. Welterweight and even Jr. Middleweight champions had been moving up and winning Middleweight titles throughout the 20th century. Historically, Michael's win was a bigger and his performance was arguably better. But, at the time both fights ocurred, Leonard-Hagler was BY FAR the bigger deal ... as both guys were bigger mainstream sports stars. All in how you phrase the question, I guess.
Michael Spinks did something completely unprecedented for a reigning LHW Champion, and without any doubt, he was a clean athlete. Larry was coming off a hard fought Championship Distance decision win over Carl Williams in the Truth's finest career performance, and was aiming for Marciano's 49-0 record. Holmes also was proved to have an awful lot left after his very ill timed match with peak Tyson. ("But Don King showed up at my door with THREE MILLION DOLLARS!" Larry, already with two Ls on his official record, did the right thing in accepting DK's lucrative challenge offer at the undisputed HW crown. It was sound business.) The Jinx had weighed just 170 pounds for David Sears, separated from Holmes I by a single bout. While SRL was amazing in coming off of five years of inactivity following a horrible performance against a mediocre Kevin Howard who decked and dominated Ray before the abrupt and possibly premature ending, he came back because he observed MMH's obvious slowing and ring wear during Hagler-Mugabe. SRL's team brilliantly dictated all the ring stipulations for their bout, which took place more than a full year after Hagler-Mugabe, and it was Marv's longest hiatus between title defenses. Hearns and Mugabe took something out of Hagler, and Ray knew it. Of course it was obvious MMH was slowing greatly while getting significantly older. Just two defenses in 1984 (Roldan, then an easy rematch defense over Hamsho), Hearns in 1984, then Mugabe in 1985. Very clearly, what the much smaller and older than SRL Duran did over the Championship Distance against a PEAKING MMH in 1983 was FAR more impressive and important than SRL-slowed and diminished MMH, Hagler-Duran having all time P4P ramifications as great as Montreal. A much smaller man was LEADING a peak MMH on the official cards after 13 rounds. Montreal/Palomino Duran, even at 145-146, UD's any version of MMH, and knocks out Hearns to unify at 147. (And by proxy, the Duran who overconfidently partied his way to peak Hearns at 154 redeemed himself by proxy with his knockdown and UD over peak Barkley at 160, in the Blade's greatest career performance, coming between Iran's twin victories over Hearns.) What Michael Spinks did to a competition sharp Holmes (just four months after the Assassin UD 15 The Truth) in their first bout, just four months after coming it at 175 for Jim McDonald, was the boxing equivalent of the four minute mile. The great Philadelphia Jack O'Brien, peaking Carp, streaking John Henry Lewis, peaking Billy Conn, the rugged Joey Maxim, the legend Archie Moore, peak Bob Foster, and EMM getting shut out over ten by the then impotent Snipes, had all proved beyond any possibility of doubt that a LHW Champion had ZERO chance of dethroning who many then believed was a top three ATG HW Champion aiming to tie one of the most exalted and durable records in ALL of boxing, and he'd proved that undersized challengers like Ocasio, Leon, and Marvis could not even compete against him. (Then, the spindly Jinx was expected to get KILLED in the Holmes rematch, yet remained on his feet and competed his way to a albeit highly controversial decision win. The Jinx proved to be a surprising good HW, just for Holmes I & II. Good thread question, but here's the difference. Even if juicing was the key afterwards, Michael's breaking of boxing's equivalent of the four minute mile had the identical impact of Roger Bannister's actual breaking of the four minute mile. Suddenly. lots of milers went faster than four minutes over that distance, and now the record is all the way down to 3:43.13, and even women have it down to less that 4:08, closing in on four minutes. (Remarkably, Bannister actually smashed Gunder Hagg's nine year old record in the mile by a full two seconds, an marginal surpass matched or exceeded only thrice in the seven decades since, and only by the fabled Paavo Nurmi previously after that record starting being kept in 1913. The current record has now stood for a full quarter century. It's only been broken by a dozen different runners in those seven decades, and overall by only seven different runners over the 41 years prior to Bannister. What Roger Bannister did is the GOAT human athletic achievement of the 20th Century for too many reasons to count. What Michael Spinks achieved against Holmes let to numerous succeeding LHW champions following suit up to HW, even if they used PEDs to pull it off. Even MW champions have now done it.) Michael Spinks did something SRL did not do against MMH. The Jinx forever changed boxing by conclusively proving that not only was it possible to win the HW Championship as a LHW Champion, but that a former LHW Champion could even THRIVE at HW after moving up from LHW. David Haye even handing history's largest ever HW title claimant his only defeat, even uniquely staggering him in the closing seconds. Without the psychological impact of Jinx-Holmes I, how long before Michael's successors even attempt what he did? And should Michael have cause the CW divison to become irrelevant and eliminated?
Spinks. The last light heavyweight champ (if WBO counts) to win lineage at heavy was 30 years ago under suspect circumstances. The last welter champ to win lineage at 160 was Cotto about a decade ago (also under suspect circumstances) and Canelo did 154 to 168 and 175 (can’t remember if lineal 175) recently.