Right now, $700 Eth can become $1400 in a few days or a week+. But the most efficient way to invest is BTC. Lining your wallet with profits is a simple skill away - day trading to USDT.
I do not think that any investment in ethereum is going to be doubled in just a week, however I think it is very likely that in the next months ethereum is going to recover some of the value that it has lost, that is why for the last weeks I have been slowly investing some money in ethereum because I want to take a position early, that way when it begins to go up I will obtain great profits.