OPK Q&A

I have been using clear blue OPKs for a bit now. I have never had a positive for a LH surge. Today for the 1st time ever I did get a faint blue line. It was about half as dark as the control line. But according to the box if it isn't as dark as the line it is negative. I am just wanting to know everyone's experience with OPKs. Best kind to use? Did they work or not for you? Best times of days to use them? I'd like to hear any and all info :)