Opks newbie

I've been actively TTC for 8 months now.. with my son's, I didn't do anything special and got pregnant straight away. This time around is a bit different. I've only been tracking cm and cp and it hasn't helped much. So I'm thinking it's time to break out my comfort zone and go ahead and try using opk. I just don't know where to start.. like which brands are better than others and where's the best deals. If you ladies could help me out I'd be so Thankful!!