For the ES symbol: I see AMP, NinjaTrader, and Discount Trading all advertising initial day trading (intraday) margins from $300 to 500. However, my TradeStation account just confirmed 50% of initial (or $6,600) initial day trading (intraday) margin. Also, TD Ameritrade is at 25% of initial (or $3,300). These are huge differences. Why? Do the guys with the super low margin requirements just suck (bad fills, no fills, erroneous fills, take your money on fills - like I read in some reviews)? What's your experience? Thank you!