From categorization and theory you can learn a couple of things about a paddle. The kayak paddle choice is in the beginning less critical than the choice of kayak, so when you start, theory and advise might be enough to choose the first paddle.
The better you are at understanding what category of paddle you want, the better you will be at comparing paddles between different categories, and probably within those categories as well. Not even a very experienced theoretical kayak paddler will be really good at comparing paddles for another experienced paddlers situation. What really matters is how the paddles compare in reall life, not how it will behave in theory, and real life depends on yourself (strength, length, stamina, ...).
That is, the absolute best way to compare kayak paddles is for yourself to test them. They are hard to compare without actually using them than is a kayak. Kayaks can to a degree be compared by yourself in simple non water tests, like sitting in them. In theory, so can kayak paddles, but what you learn from those tests is more limited. If the difference is big enough, you can say if you prefer a thinner or a thicker shaft, but even that is easier told why paddling a kayak with it than just by holding it in a shop.
So compare kayak paddles a little by holding them, weighing them, feeling them, but focus on comparing them by paddling kayak using them, and compare them in different winds and waves. Also a kayak paddle can be a large investment, although often cheaper than the kayak.
First rough categorization of what you want from the paddle has to do with your paddling technique and paddling environment. My focus is on paddles for tour paddling, which reflects in the thoughts and selections made. But even if focus is tour paddling, there are different possible choices, and there are some changes which seem to be underway:
- A tour paddle typical Euro style. Most common choice for tour paddling, good alround paddle
- An traditional style high angle racing paddle. Can be used for tour paddling, but requires a higher angle and thus demands more energy out of the paddler than a tour paddle.
- A wing paddle. These paddles are designed to grip the water very well. Has been used a lot among speed paddlers, but is gaining terrain also in the tour paddling community, although its advantage comes from the shape on the powerside of the blade, which means that techniques using the back side of the paddle blade is sacrificed a little.
- A greenland paddle. This is a traditional wooden paddle from Greenland, used in a lower angle than even the tour paddle. From those taking the time to get accustomed to it, the verdict is very often very positive.
The selection amongst the categories above do all have their followers and believers. But if your aim is tour paddling, then the high angle racing paddle is the least likely choice. After that, it is tough to rule any category out, it becomes a matter of belief and taste. However, if you are a tour paddler, new to paddling kayak, then the tour paddle is the easiest selection to get started with and using as an alround paddle.
If you are going to spend a lot of time in surf, in tiderace, and doing things like rolls, then the wing paddle is the one you should avoid selecting before you feel you have a clear picture of it and of what you want to do.
In same way as a preferrence can be found about the selection of a wing blade or not depending on what you aim to do, some settings of the paddle can be selected after knowing what is the preferred behaviour. There is a tendency nowadays for the angle between the blades to become lower, often 30-45 degrees, instead of the earlier popular settings on 60 degrees. But there is also a fair amount of people preferring zero angle. To a degree, this depends on if your aim is long distance paddling, or if you are more aiming to use it to surf. Even if you know which, I think a good choice here is to select a paddle with a shaft that can be parted. In that way, you can try different angles, and you will also have a paddle that both is easier to transport, as well as fits on the back deck of the kayak as a spare paddle in case you would exchange it later on.
The biggest advantage with a high angle between blades come when you are paddling in wind, so the paddle blade currently not in the water is affected very little by the wind. The biggest advantage with a low paddle blade angle is reducing the strain in the wrists, and keeping a symmetrical look, which makes technical paddling strokes like braces easier to learn.
Another important factor is the size of the blade itself. I for example started paddling with a fairly common blade, a Werner paddle with Shuna blade, and exchanged it to a smaller blade (se my first thoughts from my new Werner Athena kayak paddle)..
Then there is the length of the shaft. Also here is a tendency change on its way. The shafts tend to become shorter than before. 220 centimers is a common length, and then some has a shorter and some a longer shaft. But often the difference in length is small, 5 or 10 centimeters. A good way to start the selection is either to measure the distance between the fingertops between your vertically outstretched hands. An even simpler solution is to go into a vendor web site like the Werrner paddle fitting guide and let their fitting program make a suggestion.