Monero is the only one of the four that produces no public record of your payment. If privacy is the reason you are on a hidden service at all, this is the coin the rest of the decision has to argue against.
What it records
Nothing publicly readable. Ring signatures blend your spend with decoys so no input is provably yours, stealth addresses generate a one time destination per payment so the address on the chain is never the recipient real one, and confidential transactions hide the amount while still letting the network verify the arithmetic. All of it is on by default with no switch to forget.
Timing
Blocks land roughly every two minutes and a market waits for several confirmations before crediting, so ten to twenty minutes of nothing visible is normal rather than a problem. Your own wallet shows the transaction and its confirmation count immediately, which is where to look before assuming anything went wrong.
Getting it
Large exchanges still list Monero, and there are peer trades and accountless swaps from a coin you already hold. Each attaches a different amount of identity at the point of purchase. Whichever route you use, move the coin into a wallet you control before it goes near an order, because sending straight from a purchase point draws a line nobody needs.
The honest downside
Monero takes slightly more effort to acquire than Bitcoin and fewer places list it. That is the entire cost, and it is small against a permanent public record of your spending that cannot be edited or aged out.
Wallets
Feather on desktop is the straightforward choice and Cake Wallet is the strong option on a phone. Both can route over Tor. Whichever you pick, the recovery seed is the wallet, so write it on paper before putting anything real into it.
Verified addresses
anubisqdpukalgiyxlb7rtcya3u6grun2mcozonmb57c54qrt7sqh7qd.onionanubisqe2yramasw5yvlnipaknraza5rzb5uxb7zqhxuxroobvvm6aid.onionanubisqocgruji655mqys7fpafawiy2g56pjqrtecfdikhh5q4zqmfqd.onionBefore you sign in. Open these in Tor Browser only, then compare the onion printed on the login screen against your browser address bar. If they do not match, close the tab.