What is the difference between
I have noticed that sometimes
eth.pendingTransactions have some transactions that
eth.getBlock('pending').transactions does not have.
eth.pendingTransactions are the transactions that your local Geth node has, that haven't been mined to a block.
eth.getBlock('pending') is the current block your node is mining (or would be mining on). It is not a block that has been added to the blockchain.
eth.getBlock('pending').transactions are the transactions that are included in this hypothetical block.
If you are sending a transaction, you will see it first in
eth.pendingTransactions, before a miner includes it in a block.