Freestyle is the fastest stroke and gives you the feeling of being powerful in the water.
Breaststroke is a traditional stroke popular with people who like to swim for fitness. It is the slowest stroke, but that does not mean it cannot be swum powerfully and at speed.
Butterfly needs both stamina and technique, but the body movements are not difficult because you will have done many of them before in other strokes.
The backstroke is different to most strokes because you cannot see where you are going.