For those of you who are not familiar with AT, or Alpine Touring boots, they are boots that are designed for skiing AND hiking. Typical AT boot features are walk modes (the upper cuff moves freely when a lever is lifted), rocker soles (easier to walk in), small metal lugs in the toe and heel lugs (for compatibility with pin style AT bindings) and lighter weight. Their designs can vary quite a bit, with some designs most focused on light weight and uphill performance, while others feature outstanding downhill performance while still having decent mobility. For most of my clients, it is the latter category they may want to consider. Given how certain models provide outstanding downhill performance with excellent walking, should you consider AT boots as your only boots?
Performance - While older AT boots often had very poor downhill performance, this has changed drastically in the last ten year with many of today's AT boots featuring downhill performance every bit as good as the best alpine boots. An example of this is that most of the ski coaches I know use AT boots as their only boots, often while using race skis. The key is you must be selective, not every AT features such great downhill performance. (Such models are typically designed more for uphill performance than downhill.) Bottom line, be careful in your selection and downhill performance will never be an issue.
Ease of use - Ever have to walk a long way in ski boots, cross a long traverse with skis on, or have to navigate gigantic parking lots? In all these situations, the AT boot's walk modes and rocker soles give skiers a vastly better experience. (I often see skiers who look exhausted when they arrive at the base area.) Of course, it you stay slopeside at a ski area, the convenience may not be significant.
Light weight - AT boots are usually lighter than alpine boots, and in many cases much lighter. While this is more pleasant to wear, the lighter weight can come at a price. Often these boots feature lighter liners, and this can have some problems. Many use lighter weight liner materials, which tend to not hold the heel as well and pack out more when used. This is enough of an issue that a number of ski industry people I know use alpine liners in their AT boots. Still, most industry people I know only use their AT boots and no longer use their alpine boots.
Thinner plastic - This make the boots lighter, but can have some issues. They can be more difficult to widen, and the quality of the flex is usually not quite as good.
Cost - Between the need for expensive plastics, extra parts and design work, and the smaller AT market, AT boots typically retail at approximately $100 to 200 more than comparable alpine boots.
Lack of widths - While alpine boots usually come in three or more widths, most AT boots have only one width. Typically, narrowish to medium. If you have wider feet, this can be a problem.
More difficult to align - If you require significant alignment work to your ski boots (such as sole canting or cuff adjustment), AT boots may be far more difficult to have setup. While we have ways to work around this, people in this category may achieve better alignment with standard alpine boots.
Sole/ Binding Compatibility - Ugh.... here is where things get weird. While standards with alpine boots are easy, AT boots/ bindings can be more challenging. Versions include WTR (Walk To Ride), Grip Walk, etc.... , and some AT boots are not approved for alpine bindings at all. The moral here is find out what kind of bindings you can use BEFORE you purchase AT boots.
AT Bindings - Related to Sole/ Binding Compatibility, there are a number of concerns with bindings. First, it is my opinion that alpine style bindings are more reliable for safety than AT style bindings (pin style). If you are going to use AT bindings, I recommend the Atomic and Salomon Shift bindings and the Marker Duke PT (heavy but good). Both of these models use alpine style releasable toes for downhill and AT pin toes for uphill. If you only downhill ski, you can also consider just using compatible models of downhill bindings.