I strongly favour STV-PR. With voluntary voting, to improve
party proportionality and to encourage a high turnout, I propose
that the exact number of MPs elected by each district should not be
finalised until AFTER the votes are cast, and that the numbers be
in proportion to the numbers of valid votes cast in each
district. That way, there will be parochial competition
between the districts to have a high turnout.
There should be a rule that says that each district returns at
least one member regardless.
One possible refinement is for the total number of seats to be
slighty flexible, so that sometimes the total number of MPs is one
more or less, to make it easier to get good proportionality between
the electoral districts (based on the valid votes
cast). This upholds the principle of
"one-vote-one-value", and with the districts each electing about
seven members (preferably with none going below three) should make
it very unlikely that there is any (anti-proportional) unfairnes in
the representation of the parties.