The most basic warp drive is a low-level space-time contractor and expander. The technology for this drive is as old as civilization itself. They function on expanding and contacting space-time to achieve movement. These drives do not cover a huge amount of distance. But they are great to get you from one solar system to the next. These drives are largely reserved for civilian vehicles.
These are the second most powerful warp drives. They function similarly to class 1’s but have greater power and efficiency to make them cover a greater amount of distance. As a result however, these engines are considerably larger and require a bigger energy core to drives them. They are especially useful for large freight and passenger transportation vehicles.
Class 3 warp drives function via wormhole creation. These drives again are much larger in size and require an even greater power source. However they can cover a great amount of distance before needing to be refueled. They are often reserved for bounty ships, police and/or local law enforcement. Anything that would require a small crew of people.
Last and biggest warp drive class. Also the largest of the engines to date. Has a very large powersource as a result. Reserved for battleships.
Any travel between galaxies must be done through the use of warp gates as all drives are not powerful to cover the distance between them.