My choice is ethereum, because it's the closest one to bitcoin in term of transaction. Because many ICOs related to Ethereum, that will make ethereum demand keep growing and stable. Wave is good too, but it's still fluctuative i think for a moment. But both of the cryptocurrencies are good, just diverse your protofolio.
Certainly, Waves and Ethereum are good, but if you want to invest in altcoin has community better, you should to choose Ethereum instead of Waves because the community of Waves still smaller than Ethereum. The ICO market has proved Ethereum has more supporters than Waves.