You can buy either ethereum or lumens cause they have not doubled their prices yet. There are several coins which have doubledor even trippled their prices recently. I suggest ethereum because it is still one of the best coin around here. Moreover it is at tank 2 of the chart with high volume and liquidity. Their team has a strong background and the community considers ethereum as an well-known crypto. If bitcoin is called as digital gold, ethereum will be the next generation of digital money

Lumens is a little bit tougher than ethereum. I can not say an exact time when lumen will reach the bullish run but in my mind, i strongly believe that this is always a potential project which can give you more than just double your money. So, its up to you. There are many coins out side waiting for people to diving and digging