> I'm originally from a country that has proportional representation. Let me tell you - it's a total disaster.
Your former country may be seem a disaster to you, but it has been studied fairly extensively, and, among modern democracies, proportionality is very much associated with both positiive measures of function and with positive perceptions of function from those who are subject to them.
> Two-party states are better in that the population can punish party A by voting for party B and vice versa
In a mulitparty system you can pubnish any party by voting for any other party, whereas in a two party system you can only punish part A bv voting for party B, which means a strategy that makes both parties look worse but the other one by slightly more is a winning PR strategy. The results are predictable.
> The other serious issue is that each party has a completely unaccountable and opaque system for deciding on a list of representatives.
That's not a product of proportional representation, its a product of one particular system of achieving it, “party list proportional”.
Most PR advocates in the US (or Canada) are advocating systems with by-district elections, which mean you still have locally-elected by-name specific representatives, either Single Transferrable Vote (almost always this in the US) or Mixed Member Proportional.