Battlescribe gets my vote.
As I understand it, GW came down recently on a third party because it used copyright material.
Battlescribe is also now asking for sponsorship, but at a minor payout for both desktop and mobile device support I think it's worth it. The community is also pretty fast when it comes to releases, I think within 3 days the Chaos marine codex was updated with all the nuances.
I believe at some point GW will release its own app, if the age of sigmar website is anything to go off.
"Ambition is the biggest killer of Momentum"
Starting afresh with my Chaos Space Marines.
Project Log Link (Placeholder) -
Project Rebuild, Reboot, Recycle:
Stripping, rebuilding and remaking my Guard army.