There are many interesting altcoins. The most promising altcoins, in my opinion, are Litecoin, Ardor, Lisk, Verge, BitShares, and OmiseGo. They all seem to have a team of active developers and a roadmap. I always check on coingecko how active the developers are if there is a community behind that coin and how the roadmap looks like. If a coin also is undervalued (market cap below $50.000.000) it could be worth to put it on your watch list.