Read their editorial here.
In this article the Guardian spell out their reasons for their supporting the Liberal Democrats, whilst arguing that a tactical vote in certain marginal seats for Labour would be beneficial.
Beneficial for what? In the main, for a country whose Parliament more accurately represents the beliefs, wishes and ideas of the electorate. This kind of Parliament can only be achieved if the Tories - who explicitly oppose the necessary electoral reform - do not win this General Election.
Read the article. I am almost certainly going to vote in line with the ideas set out in it.
The Guardian advise strongly to vote for Liberal Democrats, but even stronger still they advise against a vote for the Conservative Party.
I am not voting Tory.