Digital OPK's are awesome! I won't be using anything but digital with our future attempts to get pregnant. I tried cheaper POAS type OPK's the second month we tried with DD and they were so annoying! I bought Clear Blue Digital for the third month and bingo, UTD. They are pricey (about $50 for 7 tests) but they take out all the guess work as you get a smiley face on the screen when the time is right. I was charting as well so I had a good idea how my cycles were (they were pretty regular, 28-29 days) which meant I didn't waste many at all. I think they are worth the money regardless though.

Good luck!