To the best of my knowledge and experience, the best investment alternative to Bitcoin (BTC) is Litecoin (LTC).
There are 21 units of BTC.
There are 84 units of LTC.
Both have a limited supply. The price of Bitcoin against USDT (highest price) is 412 USDT = 1 LTC.
Both rely on blockchain technology.
Due to liquidity effects, the price of Bitcoin always moves with the price of Litecoin.
Currently, the price of Litecoin is low, as the price has reached
76.65 USDT = 1 LTC.
This is considered the best time to invest in a currency that has value in the future.