What is Apocalypse's class? And why didn't you order the top 5 from strongest to weakest?
Apocalypse is Class 100, but he also has the ability to increase his base strength significantly.
Ordering them from strongest pose some challenges due to the exact level of their strength being mostly unknown. To order them, some guesswork must be used in addition to evaluating them based on Marvel's Handbook, comic book feats, and statements by Marvel's leadership.
STRONGEST TO WEAKEST:
1.Green Scar - likely the strongest based on statements by Marvel executives his physical power at that time was greater than any mortal's and most immortals who ever walked the earth. That must have included all other versions of himself during previous periods of extreme anger including when the Hulk defeated Onslaught. Additionally, this version of the Hulk did not fight the powerful Sentry with all the physical power available to him. This version was the lottery winner of power due to his incredible anger at the death of his wife, the unity between the Hulk and Banner personalities, and further strenthening by absorbing the radiation from the explosion.
2. Onslaught - "limitless physical strength." Onslaught was almost as strong as another monstrously strong version of the Hulk. This Hulk version was not quite as strong as the Green Scar, but was capable of delivering a blow equivalent to a nuclear strike. It's conceivable Onslaught was stronger than any others on this list except the Green Scar Hulk version.
3. Kurse - is far stronger than Thor, who is a high Class 100 character. Thor strength falls between Class 120 to Class 150. Kurse therefore was at least Class 240 before the Beyonder strengthened him further according to the Handbook. He is likely at least now Class 290, but could be Class 400. I estimate Thanos falls on the lower spectrum of this range.
4. Thanos - Thanos was a high Class 100 character prior to his death based on his ability to fight the Hulk, Thing, and Thor simultaneously, and gain the upper hand using his physical strength alone. After his ressurection, Death further enhanced his abilities especially his durability, so he was able to withstand his bout with Odin. Marvel almost always tie durability with strength in proportional terms. Thanos's fight with Omegapowerful Tyrant further proved his physical strength was significantly higher than most previous estimates.
5. Maestro - Twice as strong as the Professor Hulk who has a base strength of 100 tons.