What is the best class in team fortress 2

There is no 'Best Class' in Team Fortress 2. They all have their own jobs, so to speak. It all depends on your play style.

However, the most all-around class would be the Soldier.

The best class depends on what your good at. For example, if you like hitting and running, the scout is your best class. If you like staying back and picking enemies from a distance, choose a sniper.