Ok, I'm gonna say it: Lisk
(somebody would have said it at some point anyway)
Lisk had its 5 minutes of fame at the beginning, and nothing really happened it was hyped but in the end ETH took it spot.
The main problem with Lisk is - it is not backed by anyone really. Ethereum has the Ethereum Foundation, a non-profit Swiss organization.
Lisk has...? I don't know, something. Lisk also is lacking support IMO, behind Ethereum we have strong team of developers with Vitalik Buterin who is considered genius on top.