I've heard great things about Roderick Strong's 2015, but I think I gotta go with A.J. Excellent G1 against a myriad of opponents (Tanahashi, Ibushi, Shibata, Fale, Yano, Naito) and awesome title matches against Okada and Ibushi. Was also a lot of fun in trios matches with the Young Bucks.
Toss-up between Okada and Bryan. Bryan didn't have as much to work with but he almost always made the best of it. The Cena match in particular is an all-timer. Okada obviously has the Tanahahsi series, but he also had great matches against Makabe, Kojima, Devitt, and Ibushi. The only knock I can give him is his matches with Ishii and Suzuki were good but should have been better.
2001 as a whole is a blind spot for me in regards to what was going on in other promotions, but I think it's gotta be Austin. It's been well over a decade since I've seen the Rock Mania match, but the stuff he was doing with Kurt, Benoit, Jericho, Triple H, and Regal was always really good to great.
Only watched the tag title match, Shibata's return, Hiromu-Desperado, and the main. From what I've read about the rest of the card, that's all probably anyone needs to watch.
Jumbo or Kawada. Kobashi, Misawa, and Taue were looking like world beaters as well, but Kawada seemed the furthest along at this point and Jumbo was still playing a huge part in helping establish them.
I lean Jumbo. The Pillars were already very good but still coming into their own. Jumbo really helped make Misawa in those matches and was always a killer in tags.
Up until very recently I would have said Shingo 100%. Consistently had the highest peaks of any NJPW wrestler and for a good chunk of the year, pretty much any wrestler. But then Bryan went to AEW and had 4 MOTYC's over the course of 4 months. I keep thinking his time off after WWE should hurt his case, but I find it harder and harder to make that argument.
Toss-up between Hiromu, Shingo, and Ishii. All three were were consistently delivering in what was a very rocky year both in terms of business and in-ring presentation. Hiromu not participating in the G1 hurts his case, but he did give EVIL easily his best match of the year while nearly everyone else struggled. Ishii had impressive showings in the NEVER trios scene along with his usual singles work, and Shingo was doing great work against both juniors and heavies.
I think A.J. or Tanahashi. Both guys had feuds that were good but maybe not great (A.J-Okada, Tanahashi-Nakamura), but had terrific G1's. Tanahashi's rematch with Shibata also stands out.
Kenta Kobashi. Hokuto comes very close, but Kobashi's peaks against Hansen (twice), Williams, Kawada, and the RWTL final are pretty insurmountable. The absolute peak of his dynamic offense.
Gotta go with Ospreay. Taguchi, Cobb, El Phantasmo, Eagles, Ibushi, Okada, Tanahashi, Sabre, Dragon Lee, Bandido, Archer. Pretty wide range of opponents and he had great matches with all of them.
Okada or Omega. Even outside of their trilogy, both had great G1 runs and MOTYC's against other opponents (Shibata and Naito). Kenny also has the Ishii trilogy and U.S. title run while Okada gave Cody his best match up to that point.
Toss-up between Kenny or WALTER. I don't know if WALTER had a single match below 3.75, but Kenny had some pretty ridiculous peaks and an excellent tag run with Ibushi.