Every country has its positives and negatives when it comes to ICOs. The worst probably is United States across the board, but the ICO itself is more regulated by people looking to invest rather then the company itself. This means that running it in any country will work, but you need to follow each participating countries legal rulings when it comes to the ICO itself.
As for the best country I would say Malta just for the fact they are pushing the blockchain technology and very large cryptocurrency companies are moving there.
I think the worst ICO is China. Because China has a lot of ICO projects, many people can't see it at all. In the second half of 2017, hundreds of ICOs will be released every day in China. This is extremely rampant.