Argument: Proportional representation and coalition governments are weaker
The guy who wrote the book on comparative voting systems is Arend Lijphart.
This is the book:
Arend Lijphart, Patterns of Democracy: Government Forms and Performance in Thirty-Six Countries, 1999, Yale University Press.
Lijphart compares "consensus" democracies, the ones with proportional voting and minority/coalition government, with "majoritarian" democracies, the ones that have winner-take-all voting and single-party majority governments. Here are his conclusions:
"The overall performance record of the consensus democracies is clearly superior to that of the majoritarian democracies."
"The good news is that, contrary to the conventional wisdom, there is no trade-off at all between governing effectiveness and high-quality democracy – and hence no difficult decisions to be made on giving priority to one or the other objective."
Here's a summary of the book by Fair Vote Canada: