For me, it's Eth, ETH network is getting wider everyday, many altcoins are growing under ETHEREUM, with this have always believe in Ethereum Network. But is good holding both LTC and ETH.
Ethereum popularity cannot be compared with Litecoin. ETH is the most desired cryptocurrency after Bitcoin. Unfortunately, Litecoin is giving up slowly. Hope, it will rise again and get into the top-5 best cryptos.