If you're looking for the toughest regions, you'll be looking at Southeast Asia (SEA), China, and West Europe. These are the hardest regions to thrive in as a pro team, especially WEU given how many pros are concentrated on that particular region and how good the organizations are. China, you are looking at organizations that are basically just giving points to each other depending on the tournament for them to get the best teams on TI. SEA, well, they aren't really the best region, but the skill level of the teams in this region are basically on par with each other that's why the qualifiers are always hard to decide which team will pop off and which ones will play poorly.
Thanks, yeah I would have guessed China and Japan or Korea though, I had no idea SEA is pro (I know they play a lot but I always assumed it's just a cultural thing with cybercafes and all that). Chinese teams giving points to each other is allowed? Haha.
Koreans never had that much interest in Dota 2 since they are more focused on League and Starcraft at the time. The only Korean team I knew of that has somewhat become successful is MVP with DuBu. Even I am quite surprised that in an RTS as complex as Dota 2, the Koreans aren't excelling that much. China, on the other hand, have focused more on Dota 2 instead of League, and they're the ones whom the rest of the world are looking at when they're looking at new strategies on new patches.