Before I start comparing my spinners, let me say this: the Dynastar spinning flight system is far and away the best system I have seen. Nothing else compares. Having made such a broad sweeping statement, let me also say this: dynastar is a such a free spinning system that sometimes I think they spin too much. You can hold the dart in front of your face and give it a slight blow and the flight becomes a spinning blur. So if you like a free spinning flight this is the system you are looking for. You can get them in nylon or aluminum.
The next best spinner in terms of how freely it spins is the Spinster shaft. I do not personally own the entire shaft but I own a very unique set of darts that use the Spinster tops only for stems. One season I threw in Seattle a teammate showed up one night with spinster shafts on his darts. I remember being very impressed with how well they spun under the slightest breath. They are good looking and well made. They only come in aluminum, however.
Other spinners I have that have a good spin to them but are unfortunately less attractive are the spinners that came with my Harrows Piranhas. They are a good short length, though. I believe they are called Top Spin. I would say that the spinners that came with my Great Whites also fall into the catagory of good spin but bad esthetic. Equally mediochre are the medium all aluminum all black spinners, and while these are plenty sleek the spin is a little tight. My worst spinners are those that are nylon or plastic with attempts at spinning tops. This is not to say that all nylon spinners are bad but mine surely are. They stay on the dart but do not spin freely in the least. If you want the benefits of nylon in your stems but want the spinning action get the nylon Dynastars and ignore the rest.
Free spinning can be bad. I have talked to guys that want the dart to be more or less stable and non-moving until such time as there is a flight collision and they want the flight of the first dart to spin out of the way. They don't want it spinning in the air, in other words. To me this is not an issue which is why I like the Dynastars. In fact, I like the Dynastars so much I actually modified a set to fit my GTs:
Dynastars have other qualities that should not be overlooked. For example, Dynastars cannot be robin hooded. The flights are a molded plastic so there are no mylar layers to separate. Also the stem part of the system doesn't have anything for an incoming dart to catch on and thus robin hoods are not an issue there either. Also, perhaps thanks to their method of having such a freely spinning flight, the Dynastar flights pop off quite well so between the spinning action, the easy popcorning, and the molded plastic, the flights last a long time.
Of course now is when I remind you that I don't use spinners of any sort anymore unless on a whim. I use ordinary short or in-between static nylon stems these days and do not feel the need for spinnners. But if you are into spinners, have a blast.