Definitely bitcoin, along with either a hardware wallet such as trezor or ledger, or a simple paper wallet. Either is fine. The thing is bitcoin is the first crypto, and will forever be the most trustworthy one. Competitors will simply remain competitors, they won't overtake bitcoin.

However, XMR comes in at a close second. I think that the fact that it is fully fungible really attracts me and it's something that bitcoin lacks. I'm currently bagholding XMR for the long term and i know many others doing so too.