Based on your budget, there are two primary e-bike motor types to consider when selecting an electric bicycle: mid-drive and hub motors.
The former are installed into your bottom bracket while cranks of both types tie into them directly, whereas hub motors can be located either on either the front or rear wheel of your bicycle.
Hub motors operate independent from your pedaling system, so they can still provide assistance even if your chain or derailleur snag.
Furthermore, hub motors tend to be cheaper than mid-drive motors.