I tried both and they both have their ups are downs. Some examples

Osmand+ is really slow with map tile displaying and doesn’t make the experience smooth for me. Osmand has many more features. The maps are also a bit too chaotic imo, because all POIs get displayed together.

OM is much smoother in experience but the maps only get updated once a month. It’s extra disappointing for me because I only see my changes live after a month.

I use OM dominantly, but I also keep the other one installed in case the first lacks something

I use maps for public transport maybe and I’ve never had much luck with OM on that front unfortunately. I don’t know how well it performs in other areas though

Organic Maps does almost everything better than OsmAnd, but it also has a much smaller feature set. I have both on my phone.