My choice is Covalent Symbol and a new project that I have high hopes for, this project has 2 Moonriver and Moonbeam tokens.
Good luck with that choice. I'm not familiar with it so I wouldn't dive in with projects that I don't have any idea.
Bitcoin + ethereum are the only ones which are worth investing in for the long term.
As the always best tandem in the portfolios of most, bitcoin and ethereum has always been the best coins to hold if you want to add an altcoin with your bitcoin portfolio.