I have the Crystalyte 3540 (I believe) motor mounted on the bike and I had my Tidalforce as well as E-bikekit motor sitting nearby so thought I'd take a picture. As you can see, the Tidalforce is massive in size compared to the two others. It is truly built like a tank. The quality of the castings is very high on the Tidalforce. In second place is the Crystalyte. It is very solidly built and similar to the Tidalforce motor, is very quiet. In 3rd place is the E-bikekit motor. It's well made, but has pressed panel side covers (I believe) and doesn't quite match up to the other two. However, it is (by far) the least expensive motor and a great entry level motor. I know because this type of motor was my first electric bike motor and I'm very fond of it. It also does amazingly well when run at higher voltages, which is surprising considering it's low cost!
Anyway, here's the picture.