There is no such thing as 'the best camera'. If there was, it would be the only one sold.
This applies to anything in the mass-marketing world. There is no 'best car'. There is no 'best beer'. There is no 'best cell phone'.
The reason there's so many different models within a given company is because they are intended to fill the different needs of the consumers. Ford makes the Mustang for those who desire a sports car. They also make the Focus for those who need a family car. They also make the F250 for the contractor. They also make the E350 for the delivery company.
What you have to do is decide which model manufactured by each company best suites your needs, then compare them for function, quality and price.