Bitcoin onchain transactions are the most secure and reliable of all other mineable cryptocurrencies.
Security is provided by the Proof of Work (PoW) consensus algorithm, which allows the mining operation, subsequently each mined block contains the cryptographic hash of the previous block. As such, to modify a block, it would be necessary to modify all of the following blocks as well, which means that the older a block is, the more difficult it is to alter it.
In fact, it is recommended to always wait at least 4, 5 or 6 confirmations of successive blocks before considering a Bitcoin onchain transaction as certain, since the more blocks are subsequently confirmed, the more difficult it is to modify the block in which the transaction is included.
The howmanyconfs.com website compares the security level of a block with 6 confirmations on the Bitcoin blockchain with that of other cryptocurrencies using PoW.
For example, to get the same level of security with an Ethereum onchain transaction you need 1,258 confirmations, and a waiting time of about 4 hours and 42 minutes, compared to the 50 minutes and 24 seconds it currently takes to wait for 6 confirmations on the Bitcoin blockchain.
The differences with Bitcoin Cash and Litecoin are even wider: more than 19 hours and 120 confirmations for BCH, and more than 9 hours and 210 confirmations for LTC.
As for the other cryptocurrencies with PoW the gap widens enormously: more than 1 day for Zcash (ZEC) and Ravencoin (RVN), more than 3 days for Monero (XMR), Dash, Bitcoin SV (BSV) and Ethereum Classic (ETC), and more than 10 days for all the others.
Indeed, several cryptocurrencies take years for a transaction to reach the same level of security that is obtained with 6 confirmations on the Bitcoin blockchain, some even centuries, and some even a millennium, such as Halcyon (HAL) and Influxcoin (INFX).
This comparison can only be made with other cryptocurrencies that use PoW, so this list excludes for example XRP, EOS, Stellar, Cardano, Tron and many others. The comparison, in fact, concerns just how much computing power is required to be able to modify a mined block with PoW and all subsequent ones.
However, these data only concern onchain transactions, i.e. those that are recorded on the blockchain: on Bitcoin, for example, offchain transactions are also possible thanks to Lightning Network, and these are not recorded on the blockchain.
