In reply to ralphio: For 90% of climbers in England and Wales, 50m double ropes will make more sense. It is really only in Scotland where 60m ropes make more sense and even then only on more adventurous routes and in Winter.
These days there are plenty of options with 'triple rated' ropes that are light enough to be used as double ropes but can still be used singly.
However it also depends on what your climbing partners are doing. Pairs each having one 50m half work great but that is less common than it used to be.