I have just purchased an e-bike that came with a wide "comfort saddle". I am used to riding a hybrid with a narrow saddle, and that seat was very comfortable on long trips. Should I replace my comfort saddle with a narrow saddle, or stay with the original?
You should ride whatever you find comfortable. If the old saddle was good, swap it to the new bike.
If you intend on riding both bikes, keep eyes open for a second saddle of the same brand/model. You can store or sell the original saddle.
Saddles are a personal thing, noone can tell you what will be comfortable. Since you call the narrow saddle comfortable, go with it.
And if you don't like it on the ebike, swap back with no harm done.
It depends a lot on the seating position and riding intensity. A casual e-bike is usually intended for an upright seating position. Often the saddle will be too low and the user rides at a low intensity (and low pedaling cadence). So most of the weight will be on the buttocks. Rides on such bikes are usually too short for chafing to become painful. There is also a psychological factor that when buying a new bike a “comfort saddle” looks more comfortable and feels more comfortable when used for a short duration only.
So it depends a lot on how you are setting up the new bike and what you plan to do with it.
I completely agree with Criggie. Have a seat that is comfortable. I use a racing bike, a city bike, a mountain bike (occasionally) and an e-bike. My e-bike has a fat comfortable men's saddle. If like me, your ebike is ridden up to the 25km/15mph limit and occasionally beyond, a less restrictive but more aggressive saddle is not necessary. Sit up, peddle and take in the view.
You have to understand saddles have a size similar to a shoe that is designed to put pressure on your sit bones.
A lot of people get focused on the shape or padding of the saddle when they feel discomfort and that is a lot like buying another shoe by looking at it and not verifying that it is the right size for your foot. Most people would not do that, so you should not do that when it comes to saddle size.
Most bike shops will measure the distance of your sit bones by having you sit on a piece of memory foam. They will then measure the gap between your sit bones (e.g. 155mm). Then they will pick out saddles that are of that size. By doing this you increase your chances of ensuring pressure is put on your sit bones vs. other areas of your body that you do not want when you ride.
You should be able to go to most bike shops and ask to speak with a bike fitter to find the right size saddle. If they look at you and are confused or just say pick one out based on how they look to you, go somewhere else.
I linked some videos about how you can do a at home sit bone measurement and wrote a similar answer here that you can see too:
Before, I started seriously cycling as an adult, I never knew what sit bones were and that bike seats were designed in different widths. Once I knew more about that I found a seat that just looking at it would seem uncomfortable, but has proven to be the right saddle for me that let's me go on 50+ mile rides sometimes in normal shorts with no discomfort.
Hope that helps.