You could do worse than give this a try:

http://www.votematch.co.uk/london/

Interesting to see results - mine said I should probably vote for Ken, but Paddick rating was almost the same, then Sian Berry, and the rest were way off my views. Interestingly, of the 10 candidates, my match with Boris was the third worst only followed by Winston Something-or-other and the BNP.