There's already been a few threads on here about fixed vs. tiered and typically the answer has been go with fixed unless you trade high volume. I'm just a small low-volume (usually no more than a few hundred shares per day) retail swing trader, but I usually enter trades on a limit order (don't usually get filled immediately) so therefore I'm mostly adding liquidity. Would it make sense for me to do tiered so that I can occasionally pick up a rebate from the exchange if offered? Anything else that I'm overlooking?
I switched and that dropped my stock commissions by more than half. Again, I do mostly limit orders so I get some compensation for providing liquidity depending on the exchange. Made a big difference.