In the context of Ethereum smart contracts, send, transfer, and call are functions used to send Ether (ETH) from one contract to another. Each of these functions has its own advantages and disadvantages, depending on the situation.

First, we'll compare these three functions in a table, followed by a discussion of the scenarios where each is most suitable—and where they might not be appropriate.

Comparison Table

Feature	`send`	`transfer`	`call`
Description	Low-level function to send Ether	Safer function to send Ether	Low-level function to call a function and send Ether
Gas Limit	2300 gas	2300 gas	Forwards all gas (can be manually limited)
Return Value	Returns `true` or `false`	No return value (throws on failure)	Returns `true` or `false` and returned data
Error Handling	No revert on failure (must handle manually)	Reverts on failure	No revert on failure (must handle manually)
Flexibility	Limited	Limited	Highly flexible, can execute functions with Ether send
Use Case	Simple transfers with error handling	Simple transfers with automatic revert	Complex interactions, upgradable contracts, fallback

When to Use vs When Not to Use

`send`

When to Use:
- Fallback Payments: Use send when distributing funds to multiple addresses where some may fail to receive Ether. It's useful in situations where you want to continue the transaction even if a particular transfer fails.
- Error Handling: If you want to handle transfer failures without reverting the entire transaction, send allows you to check for success and proceed accordingly.
When Not to Use:
- Critical Transfers: Avoid using send for important transactions where failure should cause the entire transaction to revert. The failure of a transfer won't automatically revert the transaction, potentially leading to unintended outcomes.
- Complex Contract Interactions: Do not use send when interacting with contracts that have fallback functions requiring more than 2300 gas, as the transaction will likely fail due to insufficient gas.

`transfer`

When to Use:
- Simple Payouts: Transfer is ideal for straightforward payments where you want the transfer to either succeed completely or fail, reverting the entire transaction. This ensures the Ether reaches the intended recipient or the transaction fails.
- Safety: Use transfer when you want a safer alternative to send, as it will automatically revert on failure, ensuring that funds are not lost.
When Not to Use:
- Contracts with Complex Logic: Avoid transfer if the receiving contract has a fallback function or other logic that requires more than 2300 gas, as transfer will revert the transaction in such cases.
- Fallback Function Requirements: Do not use transfer if the recipient contract relies on a fallback function that needs more gas than the 2300 stipend provided by transfer.

`call`

When to Use:
- Upgradeable Contracts: Call is best for interacting with contracts that may change over time, such as proxy contracts, where the function signatures or logic might differ. It offers flexibility to forward gas and interact with any function, making it suitable for complex scenarios.
- Complex Interactions: Use call when you need to execute a specific function on the recipient contract while sending Ether. It allows you to forward all available gas, making it ideal for contracts that perform more complex logic.
When Not to Use:
- Simple Transfers: Avoid using call for basic Ether transfers, as it introduces unnecessary complexity and potential security risks that are not justified for simple operations.
- Risk of Reentrancy Attacks: Be cautious with call in scenarios where reentrancy attacks could be a concern. It requires additional security measures, such as checks-effects-interactions patterns, to prevent such vulnerabilities.

In conclusion, by understanding the strengths and limitations of each function, you can choose the most appropriate one to achieve your desired outcome effectively.

The Ethereum Toolbox: When to Use 'send', 'transfer', and 'call'