The clunky plastic things on your feet. They are clunky to ensure that the force and position of your leg is transferred precisely to your skis so you can turn when and where you want.
Depending on how well they fit, boots (regardless of brands) can either be torture devices or so bloody comfortable that you forget you are wearing them. To ensure comfort, you should spend a bit of time with a good bootfitter who will look at your feet and put you into boots that suit your foot shape and ability level. Different brands of boot, and models within brands, are made on different lasts and suit different foot shapes. The only thing that matters is the fit. Whether or not your mate likes a particular brand is irrelevant, because you will have a different foot shape. Be honest with your bootfitter. The bootfitter could not give a rats about how good a skier you are, and just wants to do a professional job and put you into the right boots for you. They also have a financial interest in not having you come back under their fit guarantee. Adjusting boots is an expense.
Most reputable ski shops will offer a fit guarantee which allows you to return to the shop an unlimited number of times for adjustment until the boot is comfortable. Comfort in the shop does not necessarily mean comfort on the hill. For example, most bootfitters will put you into a boot of a size that your big toe is touching the inside of the boot. This seems weird, but on the hill the boots will be comfortable. The difference in comfort is in part because the shop is nice and warm thus causing your foot to expand a bit, and in part because of the difficulty in precise repilcation of a skiing stance in the shop. While on the actual ski slopes, it's wet and cold thus making your feet shrink in size. Trust your bootfitter here, but if they are uncomfortable when you ski take them back to get them fixed. A good bootfitter has an arsenal of tweaks and fiddles to make boots comfortable, including packing, padding and, in extreme cases, blowing the shell out. Notwithstanding the availability of the tweaks it is better if they are not necessary.
There is a strong argument to buy on snow rather than a shop off snow, but only if the shop has a decent range of boots to choose from and has an experienced fitter. The key to this is still to find a good boot fitter and that you are there for at least a week. This way you can get the boot fitted and adjusted to your foot then go out and ski in it and take it back a day or two later and get more adjustments made to it if necessary. Any shop that doesn't offer this free should be avoided. Boots like all shoes tend to pack down and wear in a bit so how they feel on day 0 (in the shop) and after day 3 can be different and if you are on snow you can get this sorted then and there rather than skiing in pain for a week and then going back into a shop later and maybe not going back out in your boots again for weeks (or months!). A weekend isn't really long enough to achieve this.
One, apparently counter-intuitive, tip is that if your shins hurt try tightening your top two buckles. Often sore shins are caused by boots rubbing against the shin. If the buckles are tight, there is less rubbing. Another tip is to make sure your bottom 2 buckles over the arch of your foot and toe are so loose they almost come off. These are only there to ensure the boot holds its basic shape and are easier (possible) to get on. If you tighten them you will pinch the nerve to your toes and this results in numb toes. If a boot is too narrow across the area just behind the toes known as the metatarsal heads you will feel cramps and eventually a calcium build up in the form of a painful lump will appear on the metatarsal heads.
One thing that is almost always worth having is customised footbeds - individually shaped foot supports for under your feet. These improve both comfort and the boot performance and cannot be recommended highly enough.
Boot manufacturers' marketing blurb usually has a slew of pseudo-scientific mumbo jumbo with lots of numbers and indices and flex ratings and graphs and stuff. This stuff is generally meaningless. Unlike with bindings, there is no international standard for boot performance. The numbers are possibly useful for comparison within a manufacturer's range, but useless for comparing boots from different manufacturers.
If you are concerned about whether a particular brand of alpine boot is compatible with a particular binding, relax. The boot/binding interface is stanndardised and all boots will be compatible with all bindings.
Discussion of boot fitting with recommendations of fitters in Sydney and Melbourne in the following threads:
That information should probably be synthesised into here, but requires more knowledge than I've got on the subject.
Top 5 Boot fitting tips from CarveMan
Cross Country Boots
Your boots are the most critical component of your cross-country skiing system. Hire them to find what suits you. Buy them first.
Cross Country ski boots can vary in toe width, thickness and number of holes, or toe bar width and bar guage, or number and shape of grooves in their soles. However, There are compatible bindings to match each boot variety, and it is fairly easy fit compatible bindings to skis to replace incompatible bindings. For more information see under Bindings.
As with any ski boot, comfort is your first priority when buying a Cross-Country ski boot. Fit is always the key to successful ski boot buying. Wear a pair of wool or synthetic ski socks when trying on boots. A good fit is achieved when boots are comfortable and hold your feet solidly in place.
General touring boots offer flexibility for striding along with torsional rigidity for turning and stopping. Some boots have extra features such as lace covers and rings for attaching gaiters. These can be especially helpful for keeping snow out of the boots when you're skiing off-track. Once you’ve found the right boots, you can select compatible bindings. Some composite and leather boots let in water in Australian conditions. Most plastic boots are waterproof but your feet may get wet from perspiration.
Track Boots are generally a composite/leather combination offering the rigidity of a composite and the flex and warmth of leather. Skating boots are cut higher above the ankle and usually have a plastic “exo-skeleton” for extra rigidity. Classic boots are tending to also be higher cut than in the past and many manufacturers offer combi boots which use the plastic “exo-skeleton” for skating and remove it for classic. For general touring in tracks leather boots are more flexible and warmer while composite boots offer more control, support and moisture protection.
Backcountry Touring Boots must support your ankles while providing enough flexibility for forward motion. Many skiers are successfully touring the backcountry with kick turns and snow ploughs while wearing track boots or slightly sturdier leather or composite ankle height boots. For more aggressive backcountry tourers boots must be higher-cut and sturdier to also support ankles while turning and descending. Sturdy leather or composite over ankle boots, sometimes with a plastic “exo-skeleton” for extra rigidity, and lower cut Telemark boots are often used for backcountry touring. Traditional NN75mm boots (with a tongue-like extension on the front of the ski boot sole and 3 holes in its underside) are still manufactured in leather and composite materials and are a popular choice for backcountry touring. NN75mm boots are becoming hard to find new in Australian shops except as plastic Telemark boots, but are often available second hand.
Telemark Boots must support your ankles while turning and descending. Look for robust, aggressively constructed boots that also provide enough flexibility for forward motion. Telemark boots, like all Cross-Country boots except AT boots, must have a sole which bends so that the ball of the foot can weight the bindings and ski. These boots are higher-cut and more solid than light or backcountry touring boots. Telemark boots are usually plastic or have a plastic "exo-skeleton” for extra rigidity.
I am aware of only 3 brands that make tele boots. They have differing ideas on the shape of a human foot so you need to try on more than one style and brand. Teleboots are softer and more comfortable to wear than Alpine boots. Some people complain about the duckbill at the toe, its never hindered me.
I've never tried them, can be hard to get.
Alpine Touring (AT) Boots
Alpine Touring (AT) Boots resemble mountaineering or Downhill ski boots with rigid soles that do not bend at the ball of the foot. The rigid sole combines with the AT binding to give control for alpine turns on steep descents. AT boots have a lug tread for walking in snow and some have interchangeable soles for AT and alpine skiing. Alpine and mountaineering boots will fit some AT bindings. Dynafit AT bindings leverage the rigid soles of Dynafit compatible boots instead of a plate.
Links to Boot Manufacturer Web Sites 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.