Almost everyone I know seems to have a strong opinion on the upcoming reform question (and by strong here, I really mean a decisive opinion - more than just 'whatever' or 'I haven't fully considered it yet'). This in itself is interesting since Angus Reid polls indicate that 38% of Ontario voters are undecided in the matter. More interesting is that not all can explain *why* they have that opinion and fewer still are aware of any of the downsides or counter-arguments to their choice. Since I believe in an informed voting public, I thought I'd go over some of the pros and cons of each system. In the interest of full disclosure: I support the MMP system, but I'll try to be unbiased. To see the question as it will appear on the ballot and to learn the details of the two systems, visit the Ontario Referendum website.
First Past the Post
The main argument in favour of FPTP is its simplicity. One person, one vote. The straighforward nature is less confusing and less likely to keep voters at home because of voting complexity. Let's not forget the Florida debacle in the 2000 US election due to voting complexity (though that was a question of confusing ballots, not a confusing system, but it's an example of what can happen with confused voters). Being simple, a FPTP election is easier and cheaper to administer and quicker to tabulate. First past the post tends to produce more majority governments and therefore more stable governments, reducing the need for frequent elections when confidence motions fail and parliaments held hostage by small parties owning the balance of power.
On the other hand, many people feel disillusioned with the FPTP system because if your vote isn't cast for the winner in your riding, it is essentially wasted (with the exception of additional funding that goes to parties based on votes). Not only does this leave a large chunk of the population feeling unrepresented, but it can also lead to 'tactical' or compromise voting which is best summarized not as a vote *for* a representative or party but a vote against an undesireable based on perceived outcomes. This has the added effect of giving power to the media since, by and large, they provide the public knowledge of who is polling well and who isn't. Finally, first past the post leads to disproportionate representation. A party that gains 30% of the popular vote can win over 50% of parliamentary seats. One of the most striking examples of this problem is the 1926 Canadian federal election results for Manitoba where the Conservatives earned over 40% of the vote but failed to win a single one of Manitoba's 17 seats.
Mixed Member Proportional
MMP attempts to eliminate the above disparity between votes and seats by allocating a set of 'list seats' that are awarded based on the percentage of votes received on a second ballot. This second ballot also provides a disconnect between local representation and overall party values. Under this system, the electorate are now able to vote for a local member of parliament who they feel will be the best advocate for the riding as well as the party they feel will provide the best overall leadership and best represents their views as opposed to choosing between one and the other (should such a difference exist). Finally, MMP gives a voice to supporters of minor parties that might not otherwise win a seat. This is accomplished in two ways: First, having separate local and party votes enables voters to cast a ballot for a minority party without feeling that the vote is 'wasted'. Second, minority parties are more likely to win a seat and have a voice in parliament without having to beat out major parties in individual ridings. The threshold for representation in the proposed Ontario form of MMP is 3% of the vote. No minor party met that criteria in the last provincial election (the Greens were close with 2.7%), but if this system had been in place in the last federal election, the Green Party would have won around 14 seats (with 4.5% of the vote), instead of the 0 they actually had.
Despite the perception, there are a few arguments against MMP other than far flung "what-if?" result scenarios or election manipulation with decoy lists. A choice for MMP in Ontario leads to bigger (and more expensive) government with less representation. Currently the number of ridings is 107, which will be reduced to 90 local representatives. That means not only fewer people taking care of the local needs of their constituents, but depending on the way the riding borders are redrawn it could lead to poorer representation in other ways (for example, if rural ridings are merged with each other or with more heavily populated urban areas that would dominate results they lose a voice). The 'proportional' part of MMP comes from 39 seats (increasing the total number of seats to 129) that are filled with party members who are not directly elected by the public. Under this system, for those 39 seats, parties are elected but list members are selected meaning that 30% of parliament is chosen by politicians and accountable only to party leaders.
There are obviously more arguments for and against each system, and rebuttals to them all. There are also many other voting systems out there, despite the fact we'll only see our current one and the form of MMP recommended by the Ontario Citizens Assembly. In the end, all one can do is make an informed choice.