Obviously most people's first instinct would be to say "Nazi Germany". But the more I think of it, the more accurate this list seems to be:
10. The Ottoman Empire
9. The Spanish Empire
8. The People's Republic of China
7. Confederate States of America
6. Belgium (under Leopold II)
5. Democratic Kampuchea
4. Soviet Union
3. Imperial Japan
2. Nazi Germany
1. The British Empire
The criteria were:
- Body counts, of course, but not just the numbers. The percentage of a population killed and the reasons for doing so also counted
- The reasons for founding the particular entity; this probably boosted the CSA, for instance.
- Wars of aggression, including their scale and motivation.
I'm completely baffled how anyone could say the British Empire was worse than Nazi Germany, especially using the criteria you used. If I were a cynic I would say you just did that to try and get an enraged reaction, because I can't see any other plausible reason.
500 years of conquest and slaughter>6 years of conquest and slaughter.
Who invented concentration camps? The British, in their conquest of the Boer states.
The timespan isn't really relevant to how evil something is, although there wasn't an empire in 1460, and no one is denying that the British Empire did some evil things but as others have said the concentration camps in South Africa were not really similar to Auschwitz, and were certainly far less evil.
But actually looking at your criteria:
Body Counts- Well Nazi Germany started World War 2 which killed tens of millions and impoverished many more, while nothing the British Empire did came close.
Motivation- This isn't even worth explaining.
Reasoning- Well the British Empire (I'm not entirely sure, so correct me if I'm wrong) was founded to gain international dominance and to make money, whereas Nazi Germany happened because Hitler wanted a German empire. I'd say this one is less clear cut, as both seem to have happened due to a desire for more power, but then I'd also say that the reason for the founding of a regime aren't particularly important in comparison to the actual actions of said regime.
Wars of Aggression- World War 2. That is all.
Isn't it obvious which regime is worse?