If you want to rich immediately, you should invest altcoins. Let's compare both corresponding situation;
BTC price is 4 k nowadays, if btc price will increase till to 20 k, your profit will be 5x.
On the other hand when btc will 20k, it means bull will start so every altcoins will be started to pumped. Let's choose one of them; wanchain, that is my favourite altcoin. Wanchain price is 0,3 usd nowadays. When the bull starts i believe we will see 20 usd (we saw 10 usd in last bull) maybe even we can see 50 usd also. If it will reach till to 20 usd, your profit will be approximately 66x.
As a summary, i believe investment of altcoins will be more profitable.