Ski boots act as the crucial link between ability and the vehicles that take you down the mountain - the skis. Unless a skier suffers a non-releasing fall or an unnecessary binding release followed by a fall it is unlikely anyone pays much attention to these highly engineered connectors. They have almost got so good that they are an unnoticed element of skiing. Skis do a whole range of things in different conditions and terrain and so long as they are well serviced they should do this to an expected performance level. Discounting poles which you can readily ski without, it is boots that remain the potentially painful and either the performance enhancing or hindering part of the equation. To rent is to step into a swamp of unknown suffering - odours and worse still ill-fitting boots can be insurmountable barriers to pleasure and skiing performance. No matter what your level, a poorly fitted boot is sure to drag down ability.
So the alternative to renting is buying. Unlike owning and carrying skis there are endless reasons to own and transport ski boots with you on all trips, both domestic snow-dome type excursions and internationally. Buying ski boots is by no means a straightforward process but when done right these things can become better companions than a miniature of Jägermeister.
So buying a ski boot - do a lot of research or find a very good supplier or both. Stiff boots offer good skiers optimal control and power, whilst for less good skiers they can decimate ability. Soft boots are ideal for lesser skiers, can be good for off-piste or can make a very good piste skier look very ordinary. Everyone has a favourite family of ski socks (those with one favourite will likely have Martian systems in them) so take them along to a boot fitting. Make sure the seller knows how long, how well and what you have skied / ski. Don't be sold on techno-babble, a ski boot hasn't changed a great deal in a couple of decades and the chances are the sales pitch is just that - remember wheels are round, ski boots have buckles. Try many different boots on to compare the flex and fit, a shop environment is another world to a frigid glacier but getting comparisons can rule in or out a number of options. Don't even go near a mirror and flex into the boot, better to stand or walk around tapping into your smart phone. Take as long as you can to try out your preferred boots and when chosen make sure they can be returned without penalty. Go home or to the office, put the boots on and wear them for prolonged periods at tight settings, avoiding walking on surfaces other than hardwood floors, tiles and carpets (if the supplier sees that the ski boots have heel wear then they can refuse a return). Make sure the boots are comfortable after prolonged periods, not like a slipper, tight with the foot and heel completely immobilised. The less movement, the better you will ski - so long as they don't restrict blood flow or cause any pain.
Buy ski boots if you can and you will learn to love them. I arrived in a Hokkaido resort 2 years ago to see row after row of rear-entry boot - no matter what ski they had on offer, you just knew it was going to be a tough day hanging on in between the tight trees in the off-piste - it proved to be just that!