This decision still depends on which altcoin you want to sell for BTC. For me I think if you hold some altcoin and you don't sell you will make good profit that selling now.
Yes, right, we have to consider the sale of Altcoin, especially Altcoin, which has great potential for the long term, it would be better if you sell shitcoin that doesn't grow anymore to buy BTC, of course. The reason for buying BTC is very simple, because the largest and most expensive currency on Crypto BTC will generate big profits if prices rise.