Which Exchange can we use?

One of the recurring difficulties of Cryptocurrencies is the need to use multiple exchanges. How do we choose them and what are the differences between them? Let's be clear here!
Some exchanges allow the use of fiat currency (EUR, USD, GBP, etc.) with a limited choice of Cryptocurrencies, while others offer a wide range of Cryptocurrencies, but only after achieving a good level of longevity on the Market. . On the other hand, others offer only new Cryptocurrencies and of dubious reputation.
By organizing the dozens of available exchanges, we can divide them into three different types.
Currently there are:
- Peer-to-peer exchanges (among participants)
- Fiat exchanges
-Centralized exchanges