1. Connors: Certainly not the highest peak, but man, that guy was so consistently good. 12 SFs in a row (a record at any slam), 5 titles, 7 finals. Made a SF at 39, which was utterly insane for players back then. Had to play McEnroe and Lendl a combined 9 times as well as Agassi, Edberg and Borg. He also had to deal with it being switched to clay for 3 years, meaning he's the only guy to have won the US Open on three surfaces.
2. Sampras: Nearly put him number 1. May well be the best ever in terms of level. Not quite Connors level of consistency but not far off. 5 titles with 8 finals. Winning titles in his teens, 20s and 30s. Dominant over the top competition, especially Agassi. Never lost a night match. The guy was a monster at the US Open
3. Federer: Slightly behind the other 2 IMO, largely because of his lack of mid to late career success. Somewhat surprising given how well he did at the Australian Open late into his career. But 5 titles in a row is just crazy dominance. May well never be repeated at the US Open. I think he may have the highest peak there too.
4. Djokovic: I think he's earned this spot now. 10 finals is crazy. The guy is crazy consistent here. Since 2007, he has only lost before the SF twice. One was of course the disqualification. He's had to face Federer and Nadal a combined 9 times too. I don't think he has the highest level here and he's never dominated the tournament like some of the others on this list. But I find it hard to put him any lower than 4th.
5. McEnroe: Pretty dominant here, getting three in a row, 4 titles overall. Very high level. Obviously had to deal with Connors and Lendl as well
6. Lendl: I really go back and fourth between Lendl and Nadal. The extra title for Nadal is a big deal. But Lendl had 8 finals in a row and like Mac also got three titles in a row. Plus he had to deal with Connors, McEnroe, Edberg, Agassi and Sampras. Nadal only really had Djokovic
7. Nadal has 4 titles here. Could have been more but he's unlucky with injuries. Still a great champion nonetheless with a very high level