Which coins to stack to get good returns? Not talking about a price increase of a coin itself, that's another topic.
Litecoin is one of the coins that will have a good passive income. Bitcoin is another though since we are only discussing Altcoins I would recommend reading up on Litecoin since development on that coin is going on right now and the developer is getting serious about making the transactions for LTC much faster/easier to use for the new peeps.