Ice axes come in all shapes and sizes, and the range can seem very bewildering if you are a novice at winter mountaineering. However, basically (apart from a few oddball items such as Pole Axes) there are really only three types of axe: these are: Walking Axes, Alpine Axes and Technical Axes. There is much crossover between these ranges, and walking axes have been used on grade V ice climbs and leashless technical axes no doubt will have been used as walking axes, but broadly:-
Walking Axes: These are really only suitable for use as walking safety tools, ie for aiding balance, cutting the occasional step and for using in an emergency to ice axe arrest.
Alpine Axes: These are leashed axes with stronger more steeply curved picks than walking axes, making them the ideal choice for the climber doing easier snow climbs and alpine routes, or the walker who aspires to.
Technical Axes: Axes that are designed to be used without leashes for steep ice and mixed ground. Some of these may be able to have leashes fitted and some can be stripped down for alpine climbing. Some are intended for pure water ice, others for hard Continental style mixed routes and the majority can be used on either and are particularly suitable for Scottish mixed. They tend to be very wiggly and have lots of advantages if you are climbing high in the grades but a few disadvantages if you are not (such as being short in length, not very easy to plunge into heavy snow, and having no adze or hammer in some instances). Any alpinist climbing at D and above will probably prefer to use a pair of technical tools rather than a traditional alpine axe and hammer. To aid your selection of technical axes, we have subdivided them further into Scottish Mixed, Continental Ice, Continental Mixed (ie dry tooling type winter routes) and Modular Alpine (ie axes where bits can be removed to lighten them for the alps). The boundaries here are very blurred with many axes being perfectly usable for most things and certainly, anything that is good for Scottish Mixed will be suitable for harder alpine routes (D and above).
How to pick a climbing axe (if you'll forgive the pun) is one of the more difficult questions that faces the would be winter climber. What feels right to you is likely to feel very wrong to the next person. If you are unable to borrow axes to try before you buy, then the following may help.
Think of an axe as a weight on the end of a long stick. Hold the shaft right at its base (this is where you would normally hold an axe when winter climbing) and wave the tool in the air. If it feels heavy and unweildy or alternatively light and insubstantial then try a different model or try different shaft lengths of the same model. Basically what feels correct is a function of your own strength. Buy an axe that is too heavy and you will get pumped half-way up a pitch; buy one that is too light and you will curse as it bounces off hard ice! Needless to say it is rather difficult to do this over the internet...
'T' & 'B' Ratings: Ice axes are either 'T' or 'B' Rated. T rated means that the shafts are strong enough to belay from while B Rated means they are not; nearly all climbing axes are 'T' rated. Confusingly though picks for ice axes are also either 'T' or 'B' rated. 'T' rated picks are heavier duty and are designed for Scottish winter and alpine mixed climbing, but are also suitable for icefalls, whilst 'B' rated picks have finer blades and are only suitable for pure water ice climbing. For UK use we would recommend the use of 'T' rated picks as 'B' rated picks may not be strong enough for mixed climbing.