Which of the leading cryptocurrencies will become more scalable and efficient in the long term?
Will it be Bitcoin with its Layer Two solutions such as the Lightning Network and Sidechains?
Or Bitcoin Cash with its on-chain scaling solutions by increasing the block size limit?
I would like to know your thoughts about this.

I think that Bitcoin Cash is certainly an improvement on
BTC copy, but because of Bitcoin's popularity, it loses.
The increase in the size of the BCH block is also positive, but for investors the main thing is that the investment would bring income. They do not really care about the structure of BCH. As soon as all the news announce that Bitcoin is worse than BCH, then the Bitcoin Cash era will begin.