For general stepper vs servo questions I would humbly suggest googling, there are plenty of explanations out there.
Very quick summary:
Stepper motors are used for things that need to rotate continuously with starts and stops. They have very precise position control. However the control system is "open loop control" (google) so if the motor skips steps you lose all positional accuracy. They require a dedicated stepper motor driver (the Pololu A4988 is a popular choice). A stepper motor typically has 4 wires, to drive it you need to generate a train of pulses. The stepper motor driver takes care of this for you.
Servos (the hobby type) are a very small motor with built-in gear reduction and built-in closed loop position feedback. Closed loop position feedback means they will return to their set position if they are "pushed" out of position. They are also much simpler to drive from an Arduino - you just need 5V, GND, and a signal pin. The built-in Servo.h library makes it even easier from a software perspective. Servos are typically not able to rotate continuously (there are some types that can) - they have a set range (90 to 180 degrees) over which they can rotate back and forth.
For making POV(persistence of vision) what kind of motor I need to use and what should be the minimum RPM of the motor is needed?
I assume you mean that you will have a head that spins in circles. Your rpm is going to depend on your intended refresh rate. If your refresh rate is high you could do 1 of 2 things: use a stepper motor with a gearbox to increase the output speed, or use a conventional DC motor and control the rpm carefully. It might be cheaper to use a DC motor with a rotary encoder to read the actual refresh rate, as opposed to finding a stepper motor and a gearbox with the right ratio. Most stepper gearboxes I see are gear down boxes and you would need a gear *up* box.