OsmAnd is the Swiss army knife of Open Street Map frontends, but as I'm sure you'll agree on (if you've used it), it can be a bit of a headache setting it up, as well as getting familiar with it.
Organic Maps caters more to people seeking a pure alternative to Google/Apple Maps. It's the layman's alternative.
If you're a poweruser, and already familiar with OsmAnd, there's no point in switching. But in terms of getting other, non tech savvy, people to switch, it's a great recommendation!
Also a great choice. I prefer organic maps for a variety of reasons (like ability to contribute to the maps), but a lot of people prefer OsmAnd. They are both very good.
Organic Maps has fewer features and settings, a more stripped-down user interface, and concentrates on what most people use the most (find an address, navigate to it).
It is also much, much faster than OsmAnd.
Personally, I find OsmAnd too slow and clunky, and Organic Maps a bit too basic.
But I prefer Organic Maps 95% of the time.
You might be interested in Magic Earth it is also built on OpenStreetMap but includes crowdsourced traffic data. If you are in a big city then it's likely they have good data for your area.