I'd personally recommend ICOs, as some of them (not all) are pretty profitable in the long run and might generate high Return on Income. However, if you're passionate only about altcoins, I'd say:
1. ETH - it is the second one in the market and its potential is limitless; it creates various new tokens and is used for real world problems. Also, its price will surely increase, thus, better invest NOW and HODL!
2. LiteCoin - one again, high potential, decentralized, generates high return on income in the long-run.
3. Ripple - centralized, generates high return on income in the SHORT-RUN, however. You might want to consider Ripple as a means to generate income in a timely manner.