I have been using OsmAnd for some time now as I usually have data turned off and want off line navigation. Recently I became aware of Maps.me which also uses off line maps based on OpenStreetMap (OSM) data. My impressions, in no particular order, are:
Day/Night Display – Advantage OsmAnd Tie – Maps.me seems to have one rendering which is optimized for daytime. OsmAnd has both day and night optimized rendering for each style and can pick between the two based on ambient light or local sunrise and sunset. With v5.6 released recently, Maps.me now has a night display.
Multiple themes — Advantage OsmAnd. If Maps.me has the ability to change themes it is not obvious how.
Simple Interface — Advantage Maps.me – OsmAnd has an odd layout of controls and a huge number of options which makes use by a casual user difficult.
Routing — Tie. Both have issues. With some web searching and effort you can figure out how to give OsmAnd a better set of defaults to match local highway speeds. But even so, its routing is sometimes odd. I strongly suspect that both are subject to the issue of missing or bad data in OSM so both should improve over time.
Speed of route calculation — Tie. Both are much slower than web based or dedicated navigation devices.
Out of the box appearance — Advantage Maps.me. While OsmAnd has many themes available and you can roll your own if you do enough research, for a casual user the Maps.me map rendering is, in my opinion, better.
Perspective View — Advantage Maps.me. Not possible in OsmAnd as near as I can tell. This sounds like a frill but it does seem to help many people correlate what they see ahead with what the navigation system is telling them.
Speed Display — Advantage OsmAnd. Having the navigation system display the speed limit on the current road is nice. As is the ability to set warnings for exceeding the speed limit.
Lane guidance — Advantage OsmAnd. While turn lane information can be sparse in OSM, when it is available it is nice to know what lane you want to be in when coming to complex intersections.
Free maps — Advantage Maps.me. Both OsmAnd and Maps.me are open source projects and both make map generation tools available so it is possible to generate as many maps as you want on both. But the non-pay version of OsmAnd has a limit on the number of maps you can download. A casual user is unlikely to generate their own maps nor search the web for the periodically generated official map files.
Address Search — Advantage Maps.me. Maps.me has a more free form input that makes it easier to give a street and house number and get possible destinations.
Non-automotive navigation — Advantage OsmAnd. OsmAnd can display things of interest to people venturing into the back country like elevation contours, hill and slope shading, hiking trails, ski trails, etc.
Map Update Interval — Advantage OsmAnd. Neither project states an official update interval policy but OsmAnd currently updates maps about once a month (there is an experimental feature to make incremental updates much more often than that). Maps.me seems to be on a less frequent update schedule.
Installation — Advantage OsmAnd. At present OsmAnd is available from F-Droid while Maps.me is only available through Play Store or Amazon.
Distance To Turn — Advantage Maps.me. When set for using miles/feet, OsmAnd switches to feet when the distance is less than 1.0 miles. Maps.me registers miles until the distance is less than 0.1 mile which is much nicer.
Geo Intent Support — Advantage Maps.me. Neither OsmAnd nor Maps.me seem to support an address based lookup from the contacts app, but Maps.me does seem to handle location information from other apps better. For example, a location given by the Yelp app is more likely to be properly handled by Maps.me than by OsmAnd. So for getting directions to a local restaurant you will want to use Maps.me.
Stability — Advantage Maps.me. Every update for OsmAnd seems to make it less stable. On a recent trip with the latest official maps and latest version available through F-Droid I was unable to use the app at all as it kept “forced closing” (FC) (i.e. crashing) on me. So far Maps.me has been very stable on my phone.
Conclusion
I’ll stick with OsmAnd for much of my use, especially off highway. But I’ll recommend Maps.me for the more casual users who want off line routing.
Edited January 26th to add additional observations.