Personally, after tinkering with a few apps, I like the ever-popular Navionics for $15/yr. I've tried OpenCPN is a free app that also runs ENC charts, but I find it difficult to get the right level of detail from tweaking the ENC displays for light sectors, bathometric data, etc. I also have iNavX on my phone which is tempting as it apparently has ability to drag-in GRIB weather data, but it has an annoying habit of in-App purchases which brings cost to $30/year. I'm good with Navionics, at least in the US.