What is Market Execution?
This is a quoting method that's generally used by STP (Straight Through Processing) and ECN (Electronic Communications Network) brokerages.
The market execution order will get you filled at the best price available in the market. Trades requests will be placed with a liquidity provider. There will be no re-quotes, however you might not receive the exact price you requested.
So, the main characteristics of this quoting method are:
You are allowed to set your Stop-Loss and/or Take Profit levels when entering the market.
The execution of your order is guaranteed.
You have direct access to the market.
The price is provided directly from the market.
If you generally trade the higher timeframes, in which a small slippage doesn't matter, then market execution should be your choice.
What is Instant Execution?
Instant execution is a quoting method that's generally applied by brokerages operating a dealing desk. What happens with instant execution is that traders are executed at the exact price displayed on the screen.
Compared to market execution, which will fill your order at the next available price, no matter how big the slippage is, instant execution will not fill your order if it is not available.
So, the basic characteristics of this quoting method are:
You can set your stop loss and take profit orders when entering the market.
You will be filled at the requested price if it is still available. If not -> Re-quote.
The execution of your order depends on the market.
Your access to the market is indirect, through the dealer.
If exact filling price is important to your trading style, and you generally trade on smaller timeframes, instant execution may be more suitable for you.