(Separate sections for each ski type)
The long thin things on your feet that make sliding possible
Skis come in a bewildering variety of length, width, separate widths of tip, waist and tail, longitudinal stiffness, torsional (twisting) stiffness and, of course, colour. There are a variety of gizmos added to skis including flashing lights, vibration dampeners, torsion bars, magic shapes and whatever else the marketing department comes up with. The only good news is that colour does not affect performance (apart from the universal truth that red things go faster), nor, I suspect, do many of the gizmos.
As a general proposition soft (more flexible) and shorter skis deliver easier turns and faster progression for beginners. As your ability increases stiffer and longer skis deliver better performance and control. Softer skis tend not to hold an edge at speed resulting in lack of precision in turns. There are exceptions to this rule, such as park skis and specialised powder skis.
Again as a general proposition, the wider a ski is the more effective it is in ungroomed snow This is because a wider ski gives more flotation.
A good rule of thumb for ski length is that the tips should be somewhere around your nose when the skis are stood vertically on their tails. Beginners will find a shorter ski easier to handle.
Ski manufacturers' marketing blurb usually has a slew of pseudo-scientific mumbo jumbo with lots of numbers and indices and graphs and stuff. This stuff may measure real things, like flex patterns and use real SI units like Newtons but it is unreliable. Unlike with bindings, there is no international standard for ski analysis and even if the statistics measure real stuff the measurement technique will be different. One simple way to discover this is to do a direct comparison with skis from different manufacturers that are nominally the same length. There will be a significant difference. If they can't agree on how to measure a ski's length what chance is there for stuff you can't actually see? The numbers are possibly useful for comparison within a manufacturer's range, but useless for comparing skis from different manufacturers.
The ideal way to buy skis is to demo them before you buy. Many ski shops located in resorts have a stock of skis of various brands that they will let you try before you buy. This allows a direct comparison. You will generally pay a hiring fee, but if you end up buying this fee is almost always deducted from your purchase price.
When you are demoing do not go overboard with the number of skis you try. Talk to the ski shop about what you want and listen to their recommendations. It is hard to remember the characteristics of more than 3 or 4 skis each day. Try to ski each ski on the same runs so your comparison is as accurate as possible, although you should remember that snow conditions will change over the day and that as you get more tired your technique may deteriorate which will affect your perception of the ski. Once you have narrowed your choice to a couple try those two again, unless one ski is an absolute standout.
You may hear references to "shaped" (or carve, or parabolic) and "straight" skis. This refers back to a revolution in ski design that happened in the mid 1990s. The change was an increase in sidecut (the difference between the tip and tail measurements, and the waist measurement or the curve to the edges in plan view). At the same time skis became shorter. The additional sidecut made skis easier to turn, and made carving easier. Straight skis are the old style skis. Compared to the newer ones they look straight although they all have some sidecut. There was resistance to the change from old farts, but that argument was lost long ago. No manufacturer makes straight skis any more, except for racing.
Powder skis are fat. Big wide, soft, flexible boards. They tend to have not much side cut, but rely on the flex of the ski, and angulation, to turn within the snow. Turns on powder skis tend to be wider radius. Generally only worth getting if you ski NZ club fields or powder-rich northern hemisphere ski areas. Get caught in a lift line with these and you will look like a plonker.
There are many manufacturers, each of whom have a large and ever changing range. This article provides Links to Ski Manufacturers Web Sites, which should give current models and the conditions foe which they are intended. Although there are many brands there are only a small number of manufacturers as there has been significant consolidation in the industry over the last couple of decades. This is true for most of the ski industry.
Ski length chart, which should be used as a tool, not as an absolute guide. Ski chracteristics vary and your retailer should be aware of any variations appropriate for a particular brand and model.
There are a number of types of cross-country ski.
For trail skiing, the main types are Classic and Skate.
Classic skis may or may not have a patterned base. The pattern aids uphill skiing by reducing backward slide. In the absence of a pattern, classic skis should use grip wax or klister to achieve the same effect. The length of a classic ski should be more than the height of a skiier, but less than the height to the raised wrist. The profile of a classic ski is traditionally 44 44 44, although these days, wider waisted skis are sometimes used for recreation.
Skate skis do not have a patterned base and do not use grip wax or klister. The length of a skate ski is normally about 10cm shorter than a classic ski.
For off track skiing and touring many people choose skis with steel edges for greater control and security on hard snow. These skis tend to be wider (and obviously heavier).