"Ok, what about poles?"
Poles, like skis and boots, are optimized for different types of skiing and snow. Since you need different skis, boots, and bindings for each different kind of cross-country skiing, naturally you need different poles as well! Well, it's not quite that bad: Basically you have cross-country poles, which are longer than downhill (Alpine) poles, telescoping poles which are combination of cross-country and downhill, and skating poles, which are even longer and very light (and expensive).
There are three main parts of the pole: the handle, shaft, and basket.
- Handles should have straps. Straps are needed in the backcountry to allow your arm to follow all the way back when poling. However, when going through thick brush or trees, remove the straps to prevent a severe shoulder injury in case the pole gets caught in brush.
- Shafts should be light, rigid, and durable. The lighter they are, the better they feel and the less work you do. Rigid poles are more efficient at transferring your push on the handle to the snow. Shaft materials include aluminum, steel, fiberglass, and "exotic-glass" (Todd's term). Steel is way too heavy. High strength aluminum and fiberglass are usually suitable for backcountry touring and are reasonably priced. Cheaper poles have a cylindrical shape, and more expensive poles have a tapered cylinder shape. The taper decreases the "swing weight."
- Baskets are round (cross-country), butterfly (skating), or hybrid. Round baskets are good in soft snow, butterflys are best in hard packed snow, and hybrids combine the best features of both.
Cross-country poles: Fiberglass poles are the best for backcountry use. If they break, you can usually make a splint from small branches and wrap electrical tape around the pole. Aluminum poles are harder to repair. Watch for poles on sale. The pole basket (at the pole bottom) should be either round or a hybrid between round and butterfly shape. The straps should be easily adjustable, even with gloves or mittens on. The handle should continue about an inch above where the strap comes out of the handle.
Telescoping poles are used by ski mountaineers because they can be lengthened to cross-country length for the uphill, and then shortened to Alpine length for the downhill. Telescoping poles usually have a twist grip to loosen and tighten. They are the most expensive of all poles. They can also be extended and connected together for use as an avalanche probe. The twist lock type has been a little problematic for many skiers. The flick lock and oval shaft types are better and costlier.
If you're doing Nordic downhill with Cross-Country skis on lifts, Todd recommends using Alpine ski poles. The length puts you in a better body position. It's also safer - less prone to shoulder dislocation. Nordic downhill is tough on poles. Todd recommends getting cheap poles, rather than whacking up more expensive adjustables.
Skating poles should reach somewhere between your lower lip and upper chin. Mark Nadel says the exact height varys depending on personal preferences. You might try renting a pair to determine your best length. They should have an "exotic-glass" shaft, butterfly baskets, and carbide tips on the bottom. Exotic-glass (Todd's term) is an epoxy resin with fiber types that are more exotic - like boron and aligned carbon. The fiber windings can be aligned to enhance the pole's strength and spring. Exotic glass is usually best, but its price relegates it to the rich or racers (who aren't necessarily rich, but it's the price of competitiveness).