Boot Selection

Comfort

Comfort is the most important factor when choosing a boot and an ill-fitting boot will, at best, make your day on the mountain miserable. Various issues can stem from a poorly fitted boot such as foot pain, pressure points, and nerve damage; just to name a few. Always try on a boot before you buy and be sure to walk around a bit in it. If you feel your toes just slightly touching the end of the boot, that is ok... but they should not curl or feel squished. Try on as many boots as you can because a boot that is comfortable from the moment you put them on until the moment after you've taken them off should be the winner. Don't be afraid to shop around at several shops in order to get the most variety.

Stiffness

Stiffness is a key factor that will vary with your style of riding. If you are new to the sport, you will want to consider a softer flexing boot that will allow a bit more play at the expense of responsiveness... that extra give will allow you to make more mistakes without always suffering the consequences. As a boot gets older it will tend to get softer, so even the stiffest of boots may end up settling as medium-stiff after a season or two. Most riders will want soft to medium stiffness, allowing them to steadily progress on the mountain. Stiffer boots are harder to come by and are mostly used in the backcountry or for riders looking for complete control. Due to their rigid structure, they are often less comfortable so it may take a while to find a stiff boot that fits your foot well.

Sizing

Boot size goes hand in hand with binding size. When your foot is on a  size boundary, you'll need to ensure that you have bindings that will accommodate the boot. As an intermediate or advanced rider, you will also want to consider your preferred stance on the board as well as your board width to ensure that you won't have any toe or heel drag when riding. Large feet often require mid-wide or wide snowboards to accommodate them and it's worthwhile to bring your boots and bindings in when shopping for a new board. In general, you want your toes and heels to hang over the board about evenly (favoring heel hang over toe hang) and only slightly (a couple centimeters).

Durability

As you begin to pack the mileage on your boots, durability will become quite noticeable... this is especially true of the stiffer boots. Some boots last around 30 days of riding while others have been known to last for over 100! Of course, your style of riding will heavily influence how long your boots last, but remember that they are equipment serving a purpose and should be replaced once they stop performing to your needs. Having a boot blow out on you while riding on the steeps or in the woods is something you will want to avoid at all costs... trust that. If your boots have lost most of their original characteristics, then consider riding with them on your more leisurely days and replace them with a performant boot for the times where you really need it.