Gronze is still only an website, though, correct?
@laurenjk, I was avoiding giving an answer to this on the basis that I have no idea what the best app is and you provided no criteria on which to frame such advice. However, There is a Gronze app. Details can be found on the web page, somewhat surprisingly by clicking on the menu item 'App' on the top menu bar of the website. It has been available for a while. I have used it, and it provides a quite effective map and contact details tool for all the Gronze content, or works as a portal into the website if more information is required. Not available yet for iOS, but certainly for Android.
I have used
Wise Pilgrim on the Portuguese and Sanabres routes. The developer is a forum member, and is quite responsive to questions and comments. Issues that I had with the Plata app on the Sanabres were fixed overnight.
My personal view is that there is no one best app. In regards to accommodation on the CP and the VE, I used a combination of
Wise Pilgrim, Gronze (app and webpage),
Brierley, booking.com and Google Maps. I would never have found all the places that I did stay with just one app.
I also have the Buen Camino app loaded, but haven't use it much at all, and have no comment about it. The interface might suit you better, so it's worth checking out.
You also don't indicate whether you will have a data connexion continuously available, or only connecting sporadically. This might be a factor in your consideration along with aspects like whether the information is kept current, whether you want to see feedback from others, links to other tools like WhatsApp and booking.com, whether you want to navigate through a list or use a map.