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.
Then why you wanted to convert that Bitcoin to altcoins when you are planning "IN THE FAR FUTURE"?
bitcoin is the best currency if you are planning long term and also try not to have comparison to this 2 currency , if you really wanted to put money in altcoins then better to divide into Solana and Ethereum each have 1 k .
then from there you may have 2 options of making money in the coming years.