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.
you can divide it into 60% ETH and 40% SOL. These two altcoins have increased significantly and many interesting projects have been established on these two altcoins and both are very attractive and in demand among the world crypto community.
Since Ethereum and Solana, are his preferred altcoins there's nothing stopping him from investing in both of them, they're two top altcoins, and they're both looking good to give massive ROI in this bull run. You just have to consider the high gas fees of Ethereum, other than that it's a reputable crypto to invest in, also Solana, has a faster network speed and it has been building momentum since the last quarter of 2023. Both are looking for ETF approvals, which will further make their prices to surge if it happens, especially that of Ethereum, which might be approved in this year, so they're both good choices. I'd rather let the OP decide the percentage for himself, that is if he wants to invest in both of them.