I use IB. Low fees but you have to pay for market data now ($10/month). Still worth it if you trade regularly, especially options.
When I was first learning options, I sold a ton of at the money naked calls on volatility. The Greek crisis hit the news and I ended up way under water. At the end of the day, my phone started ringing with dozens of email notifications as IB was force liquidating my positions according to an automated algorithm. Said algorithm is apparently designed to make the very worst possible decision from a tax perspective. I had a very stressful next day trying to gather the smoking ruins of my portfolio back together and escape to trade another day. It was my fault. When you place a trade in WebTrader, you get a confirmation screen that notes what your new initial margin will be. If you use too much, or close to, you get what you have coming to you.
I ultimately came away from the experience a few thousand dollars up and with a lot more grey hair. The good news is I learned a lot and have practiced reasonable risk management thereafter.