I found through trial and error the best real-environment feel, at least to my tastes, is a Prophet chart and CQG Trader DOM. As to the former: near as anyone can tell, Prophet sold the remainder of their business to TD Ameritrade. Ironically, you can use Prophet in a sub-class section of the thinkorswim desktop application free to download if you complete their TD Ameritrade's application process.
As a demo, CQG is better about re-distributing simulation license keys for their software, whereas the trend elsewhere is to issue it once; follow-through with a sales call when it expires (but really you'll go to them); and if they don't make a sale or open a new account, it's not impossible to receive another, but the bitter taste over the ordeal lingers.
Also, be careful of hidden fees. Trading NinjaTrader live, is a scalper's worst nightmare. If you don't like Prophet, use NinjaTrader's charts for free.
CQG Trader live, if you can find a firm that offers it, has competitive fees. At Amp, it's .25 cents a side on the table and definitive.
Amp's commission structure is also competitive. You could find better, but you might sacrifice quality in service and technology for it.
I'm generally not a fan of crash and burn irresponsible margins, but if you start a 10 thousand dollar account and trade 10-15 contracts, you'll move the market placing trades slightly, which is a different trading environment than trading live with one lot or sim, and you'll likely blow an account trying to crash course you're way out of it.
So in the beginning, try Amp. Then when you're timing is better, transfer to say Dorman, directly.
As a side note, I don't generally disagree with other posters here in concern to percentage-wise, unnoticeable slippage in ES, but the instrument is by degrees losing its liquidity. Any class of a second chart during the last few weeks during Street hours has been dispersing. That's likely to change, but it could continue to get worse. Very few winning trades in that instrument as of late. People are looking elsewhere.
Best of luck to you.