I’d say Organic Maps is quicker, if you know a specific information at a specific place needs to be updated, whereas StreetComplete is better for finding out where on the map information is still missing.
So, StreetComplete basically sends you on various ‘quests’ to check information on-site. It’s more intended, if you’re generally interested in contributing, but makes it rather fun to do so.
There’s two alternatives currently in development, inZOI from the PUBG devs, and Paralives from a smaller indie studio.