I’ve heard that some direct drive hub motors display a condition called “cogging”. The review of the latest model Stromer bike stated that the company had worked on the problem and it’s now a non-issue. I personally have not ridden a direct drive bike; perhaps some others could give some input.
Most direct drive hub motors have cogging as mentioned above. Some center drive motors have a very slight resistance, although this doesn’t impact coasting per say. To answer your question more specifically a center drive motor would generally coast the easiest becasuse the motor is independent of the wheels turning.
All the drive systems have free wheel mechanism that allow the ebikes to coast just like any regular bicycles. All except one, the direct hub drive, some have more "cogging" than others. Examples of direct hub drives are the Stromer, BionX, Vintage, Stealth, Rimac, magic pie after market kit.
If I compare my geared hub motors to bike hubs off the bikes, it takes more force (a lot more!) to turn the axle with the fingers with a motor. With the wheels mounted, when I spin the wheels by hand, the plain hub might spin 5-6X longer than the motor, but the motor will spin for 10-15 seconds. An all-out comparo done by physics students would indeed show a plain hub coasts further. However, in an actual riding situation, the drag is negligible on coasting. Tire size, tire pressure, and wind are more important. If you can, test ride the bike.
I'm more concerned about how easy my bikes are to pedal un-powered. My geared hubmotors and my BBS02 pedal pretty nice. I did test ride a Stromer and Evelo ebikes with direct drive motors last summer. The Stromer rep warned me that level 1 pedal assist was just enough to overcome the motor drag, but I found both bikes on my test ride fairly easy to pedal with no power. I liked them. These are smaller motors. I've read that the big 1000-3000W direct drive kits are very hard to spin.
I am not a strong pedaler at all, by the way, but I have a 55 pound fatbike with motor that I don't mind pedaling unpowered at about 10 mph on level ground. With its original tires, I could barely move it. It's all about tires.
My geared ebikeling wheel has almost no drag. It better not, the battery failed after 11 miles, and the motor/controller failed after 60 miles. But I pedaled home the 23 miles with no more problem than usual. Better, since I was light, carrying only an 18 lb battery .
In my experience, a geared hub has the best of both worlds. A pretty good coasting hub and easy to pedal unpowered. Two sides of the same coin (coasting and pedaling unpowered)
Granted, mid-drives coast better but they are not super easy to pedal unpowered (e.g., Bosch, may be Brose or Shimano is better in that regard).
When I was training for my cross country ride, I used to ride a Haibike Full Seven S Rx (now owned by @rich c ) unpowered for 10-15 miles.
If your bike has a sprocket equalizing system, pedaling such a bike for long distances without any assist is very difficult.
I have a Haibike Trekking S Rx and it coasts better than the Stromer ST2. But, I have not replaced the brake pads on my ST2 in over 5000 miles while, my Trekking S Rx has consumed a set of pads already.
In short, each system has its own pros and cons. But, mid-drive E-bikes do coast better.
@e-boy definitely the new Active and Active Plus systems are incredibly easy to pedal without any assistance and coast Rear hub units like on the Easy Motion also makes life super easy. In looking at a bike don't forget that tire width and components like hubs, gearing systems all have an influence, so don't forget to take that into consideration when choosing a great bike.
To me coasting only happens when on downhill grades and on any bike e or otherwise is counterproductive to maintaining forward momentum efficiently. For the most part the extra weight of a modern e system on a bicycle will take hold and overcome any significant drag while not actively pedaling on downhill grades.
That said, my first experience with a direct drive hub was a Golden Motors Magic Pie years ago and it would not coast down a hill any faster than 24 mph due to the aforementioned cogging effect as a result of the 20mph limit via the controller. I was reluctant to try a dd hub again but I discovered that with a properly set up controller and some Statorade the two I have now show no signs of cogging and will freewheel with the best of them.
Because mid drives don't have any effect on the bikes hubs when not under power any of them should coast as well as any bicycle. Geared hub motors will freewheel also.