opk - digital or not

After two years of ttc on our own we've decided to up our chances by using opks. I already have the really thin ones that come in little foil envelopes but am wondering if the digital ones are better or if they're both good. I'd love some feed back and opinions. I'm in the middle of my period right now so once it's over we are starting the opks. Thanks in advance for any and all feed back!