I have around 2k USD of btc and I wanted to swap it for something but I can't decide whether to buy eth or Solana both seem extremely promising in the far future.
If you have 2k usd worth of bitcoins then you keep your bitcoins and never buy others coins by swapping those bitcoins. But if you really want to go ahead with Ethereum and Solana coins then you can buy your earnings using DCA method. I don't consider Ethereum and Solana as bad for investment but I forbid buying all these coins by selling Bitcoin.