Well, there's how much damage a Pokemon can tank before they faint, commonly referred to as "health". There's how much damage they dish out with physical attacks as well as special attacks, and how well they resist those types of attacks as well. And then there's speed. Those all combined make up a Pokemon's "statistics", and as I'm sure you can guess, each Pokemon species has different levels in each of them.

For example. Charizards like Blaze are quite good at using special attacks, and pretty fast. They're also decent at resisting special attacks and at using physical ones. They aren't so good at resisting physical attacks and their health is so-so, though. You have to take all that into account, plus type, plus level, plus the attacks they and your opponent know.

[You literally asked for this, Rainbow.]