In reply to TomAlford:
The best layering 'system' in my opinion is one that can cope with the widest range of expected temperatures / conditions and activity with the least amount of taking on and off that suit you. At some stage we are likely to get too hot, too cold, damp so the system has to keep you at a reasonably comfortable state for as much time of the time as possible. Different temperatures / conditions / activity will require tweaks or changes to the 'system'.
For example I often use a lightweight hooded softshell. Sleeves can roll up, full length zip opened, pocket zips open to vent ( assuming nothing to fall out ). When temperatures / conditions become cooler and or activity reduces I can roll sleeves down, do zips up, put hood on, cinch drawcords closer etc. It can cope with showers.
Underneath I will have a light weight high wicking layer that is also adaptable. This may be a long sleeved one with a deep venting zip, sleeves I can roll up and thumb loops for when I feel colder or possibly a short sleeved, zipped version.
For me these work well most of the time when walking, scrambling or climbing in the UK and also summer alpine. I might use a different weight base layer or softshell depending on the activity / conditions and temperature range such as for UK winter climbing. However, sometimes I will need to take hard shell clothing or a belay jacket. Sometimes I judge it wrong and get too hot, too cold, too wet but that kind of goes with the territory.