Of course everyone wants their expenses for trading to be as close to zero as possible. If you're trading as a business, not as an investor, I feel you have to be concerned the the entire offering, including price. Which firm offers the best package of price and service that allows you to concentrate on making money and not get distracted with other issues. What "deal" offers both piece of mind and the highest net profit at year end. If one online firm is very inexpensive, but only cares about the market maker that pays them for order flow, that may not be best for you. If another one is very "cheap", but you spend one hour a day on problems or issues with your account or platform, and not trading, what value would you place on personal service?
Always looking for the "cheapest" commission does not always get you to what you're looking to achieve, a more profitable business.