An interesting question in some respects, since it both highlights what I consider to be defficencies of our electoral system plus a natural dillema of who to vote for in the face of the current situation.
Firstly, I live in Southend West, a very hardcore Tory area. The Lib Dems are the only party with a realistic opportunity to take the seat. In recent years, since Blair, the Labour vote has been better but it's simple decreased the Lib vote without greatly affecting the Tories. Even back when the Labour party was closest to my views (something they can't be said to be now, and it's not me who's changed) it would have been pointless voting for them where I live. So, point one is that for years the objective for people like me was more to get the Tories out than particularly to get the Libs in.
Point two, I don't really feel any of the mainstream parties reflect my point of view. I believe that voting for those over the age of 18 should be made mandatory but that a 'no vote' option should be included; this would show the extent of disenfranchisement.
Point three; the Americans have the right idea in so far as one should be able to vote for ones representatives at a local level apart from the party one chooses to govern the country, otherwise, if you hate your local candidate, you have to vote for them to get your party into power.
In the real world, I imagine I might vote either Green or Lib Dem, depending on how I feel the election as a whole is going. I want Blair out, but don't want the Tories in. It's certainly not ideal!