This great website lets you compare policies from the six major UK political parties on a range of key issues: Health/NHS, Economy, Immigration, Europe, Welfare, Democracy, Environment, Education, and Crime. Pick the ones that matter the most to you.
Since you do it without knowing who wrote the policy you can be unbiased. It looks like a lot of people are surprised by their results.
It takes a few minutes if you want to read the policies properly, because some of them sound similar at first. But it is worth the time.
Take the survey at Vote For Policies to find out who you should be voting for.