I think you have already passed the best investment opportunity as for late 2018. In December the prices were extremely low, but as for now the prices are still great. If you forget ETH was around 1400 a year ago, so I think it is still great.
Right when the end of 2018 the market has dropped dramatically for quite a long time and it really must be an opportunity to buy quality Altcoin and then survive in the long run.
ETH is indeed the best coin for the long term and the quality is undoubted, not infrequently the coins fall, so now or tomorrow we will start investing if we are right in processing it will certainly succeed.