In reply to ire: As others have said, the definition of softshell is rather vague and there probably cannot really be a 'best'.
First, there is a massive range of climates and activities that come within the wide remit of 'mountaineering and climbing' and secondly individuals have very different metabolisms and preferences.
As others have said that means that what is 'best' for the Alps, will not necessarily be the 'best' for either Scottish Winter Mountaineering nor general UK hillwalking.
Also, it is worth being aware that 90% of what is on the market is not specifically designed for UK use. The vast majority of jackets are designed for use in North America, Continental Europe or Scandinavia, all of which are considerably drier than the UK. Aslo, probably half of them are designed with as much of an eye to fashion, style and colour as to performance.
The reality then is more comprehensible:
There are loads and loads of softshells that function predominantly as windproof fleeces which are superb for walking to the pub. Some of them are also pretty damn good for general Alpine (and other cold, dry & windy weather) use varying from the bargain Decathlon Bionnassay to the top notch Arc'teryx Gamma.
There are Parmo softshells which are great for steady hillwalking in all weathers.
There are then various shelled Pertex softshells. These include the classic Buffalo & Montane 'pile & pertex' tops which serve well in very cold and damp conditions. However, they also include shelled micro-pile tops such as the Rab Vapour Rise and Marmot Driclime which are felt by many to provide the 'best' option for those want to completely discard hardshells. See
http://andy-kirkpatrick.com/articles/view/the_best_softshell_in_the_world for an excellent justification.
Which option you may want go with will depends on personal preference, what other clothing you have and the balance of activities.