In recent years, proportional representation voting systems have moved from being an interesting political theory to discuss to viable political options for American elections. Thus, it becomes more important to make sure that one implements the best system for a certain level of elections.
Cumulative voting is easy to explain briefly, and thus a good choice to illustrate a PR system.
But preference voting is the system local activists should seek to implement. Here is why. Some people believe preference voting is too complicated, but the evidence strongly suggests otherwise. With cumulative voting, it's not so easy. We have already seen this happen in some cumulative voting elections, like the 1991 city council election in Peoria, Illinois, where two black liberals split the black vote.