MomMed vs Wondfo

I know these aren't positive but I'm about 4 days away so testing to catch it. This is first time using MomMed but I've used Wondfo a good bit. now I'm confused as I dipped the MomMed for a couple of days. Because I wasn't sure about them and they don't seem to change so I decided to use one of the few Wondfos I have left. Why does it seem that the Wondfo looks a bit darker and the MomMed not? How reliable is the MomMed brand vs Wondfo brand? This app also reads the Wondfo as darker than the MomMed. So now I'm confused as to which on to trust and when I would actually ovulate.