How do you know unless you have used all of those platforms and tested them out? Have you scalped with Etrade, Schwab or TDA and timed them?If you are more of a scalping daytrader who needs trade executions as fast as possible then a broker like Lightspeed in my opinion is usually best whereas brokers like Etrade Schwab and TD Ameritrade can certainly lag at times and for rapid fire scalper type traders that is usually unacceptable
I don't day trade or scalp but my executions using one of them were all instantaneous as far as I could tell, without using a timing algorithm.
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