I recently read a forum discussion comparing commissions exacted by various online brokerages. The person who started the discussion intended to switch his account to the brokerage with the lowest commissions.

One brokerage had offered a particularly low commission rate for a group of traders, a rate not available to the general public. That rate was quite attractive. The trader was leaning toward that brokerage. However, the trader wasn't asking enough questions. I'd heard through the grapevine that some using the brokerage with the attractively low commissions experienced problems launching the platform some days. They sometimes saw funky profit/loss figures for the day or had order entry problems if they didn't launch the platform in a particular way. Some reported delays in opening accounts. All reported that the platform was much clunkier than another frequently used online platform.

Even the more frequently used online platform experienced trouble on the flash crash day. However, I didn't hear about many problems on flash crash day with a third platform, one that offers very little in the way of analytics and fewer order entry choices. Who knows: perhaps that's why the platform appeared more stable that day. However, this third online brokerage charges a minimum ticket charge, so that small trades suffer from proportionately higher commission costs.

In the wake of FINRA audits of some brokerages, the more preferential margin treatment at one brokerage was eliminated. Some traders who have formed trading businesses, forming corporations, find that they're now charged huge monthly fees for live data feed since they're considered professionals. Some platforms offer futures and some don't. Some usually higher commission platforms assign a trader a particular broker who can be consulted: many don't.

Obviously, low commissions are important, but they're not the only important aspect to deciding on a brokerage. Low commissions can make or break trades, and can govern the flexibility with which a trader can adjust. However, equally important in my eyes is this consideration: Is the platform stable? Closely behind in importance is the ability to set meaningful alerts and send them to a smart phone and to set flexible contingent orders. I don't care what the commissions are if I can't sign onto my platform, or if I can't put alerts and just-in-case-of-catastrophe orders in place in case of . . . well, a catastrophe.

Next, how difficult is it to reach the trading desk if the platform goes down? As painful as May's flash crash was, it offered many of us an opportunity to answer these questions. Many traders were surprised to be locked out of their platforms. If they could sign onto their platforms, they may have attempted placing or cancelling a trade, without the ability to verify that the trade had been placed, filled or cancelled. Many received a recorded message when they tried to reach the trading desk. That was a horrendous afternoon for all traders except those in pure long puts, but such complications heightened the horror for some traders.

Until recently, I traded on two platforms. On one, I experienced these problems. On the other, I was able to reach my broker and place trades, even spread trades. I paid for those abilities. That platform charged a minimum ticket charge that made it difficult to test new trades in small contract sizes or to use small numbers of options to hedge delta or other risks when I wanted to adjust.

If you're considering opening an options-trading account or changing platforms, commissions can't be your only consideration. I would talk to the contact person about what the platform experienced during the flash crash. I would talk to that contact person about other matters, too. What securities do you trade? Does the platform offer those securities? What type of trades do you prefer? Does the platform offer the ability to easily place that trade from the platform? One I used offers a custom tab that allows me to design just about any kind of options trade I want, while at the other, I sometimes had to leg into a trade or call the broker to set it up for me because there was no ability to enter that trade directly from the platform.

Will you be trading from home or will you mostly be accessing your platform via its mobile version? The mobile version of one platform I use doesn't allow spread trades at all. Another presents some difficulties for those using Apple products, requiring some workarounds.

Do you like to watch price charts with indicators or profit/loss charts with Greeks? Some platforms are better than others at providing either of those types of charts or at least a listing of the Greeks of the position. Just last week, one trader questioned a community of traders about how to monitor the Greeks of a position on one platform. The community's answer? You don't. You can't. Instead, you pay for a separate risk-analysis charting program and load your trades into that platform to be monitored.

It should be obvious that there's no "one size fits all" for online brokerages. The trader who has a $2,500 account, trading in one or two lots, certainly doesn't want a brokerage that charges a minimum ticket charge. The trader who trades a $400,000 account and has purchased a proprietary profit/loss charting system that integrates with many online brokerages may need only to balance the lowest commissions against the most stable platform with the best fills. The middle-of-the-bunch trader with a $25,000 account trade who trades actively from work, adjusting frequently, needs a mobile platform with great alerts, while the one with the same account size who can't access the platform during working hours needs flexible and reliable contingent orders. Are you an inexperienced trader or one who doesn't adept well to new software? If so, perhaps you'll need some hand-holding now and then, and you don't expect to make any adjustments after you enter a trade, wanting an either-it-works-or-it-doesn't approach. Perhaps you need an online brokerage that allows you to connect with a specific broker.

If you're thinking about changing brokerages or setting up an account, think about the size and types of trades you'll enter and the conditions under which you'll trade. Before you ever contact the brokerage you're considering, set up several trading scenarios that are likely for you, and ask about those with as much attention as you give to the commissions. You may find that the inability to trade futures on one platform or to trade spreads on a mobile version of another are deal breakers for you, no matter what the commission rate.