Well, the combination of a weak up front Tories, Strategically flawed yet lively Lib Dems and Tiring and idiotically stubborn Labour means you have a rather poor line up all in.
Yet, Because in terms of policy I agree with the Tories over the Lib Dems and Labour I will prefer to vote for them, however, as I live in an area where people would rather murder family members then vote blue, then I may end up voting Lib dem as a protest.