Personally, I use Maps.me for simple tasks like finding street, shop or other POIs. OSMand is my favorite tool when navigating during cycling trips because of far more advanced rendering options. Both apps are great.
Osmand, as the name implies, is Android only, though. Not a problem for me, since I use the fdroid version, but OP was specifically asking for an iOS app.
EDIT: as below, I stand corrected. Please ignore my false statement above.
EDIT: as below, I stand corrected. Please ignore my false statement above.