What is the broker that you recommend for day trading US stocks?

Hey guys! I new in this activity. I've been using the IB demo account for about the last 4 months. Sometimes I felt that the filling is slow, but I thought it was just normal. I mean, nothing related with the broker. However, I've just read that the IB speed execution is not good for day trading if your strategy need a very fast execution. So, I really appreciate if you guys can recommend some brokers with a great speed execution base on your experience.