I've used TD Ameritrade for about 15 years now and never had a problem. Solid speed of funding and reverse. I would have probably recommended etrade as they used to have much cheaper trading fees but it looks like they are equal now (TD lowered, etrade higher).
I don't trade anymore. I got bored with it. Anything I buy is a super-low cost ETF (.08 fee) that Ameritrade lets me buy and sell for free as long as I hold it for a year. And then, any profit is completely tax free for someone in my tax bracket. It's the cheapest diversification option following traditional investment philosophy that you can find.