Actually, a lot depends on the purpose of your project too. If the Uno and the servo are together in a stationary platform, e.g. a box that does not move as apposed to a robot that goes everywhere, then the best power source would be a mains adaptor. (AC to DC, like a phone charger), because your Servo needs power the UNO can't deliver with a battery. Note also that the Servo should be connected to the PWM pin (Pulse Width Modulation).
See my website here:
https://www.professorcad.co.uk/appinventortips#TipsArduino
See this Forum Topic, which uses a similar servo (you will need to read the latter part of the Topic about power).