there is no such thing as best. do you need to write your own algos? what kind of charting do you need? what broker do you prefer and how much of commissions will you be paying? what is the acceptable latency. just some questions to determine your style of trading.
Id say stay away from ig markets,they are a bucket shop broker.my personal experience with them is very negative.
TT and CQG are the most famous one. TT has just broken it with his new TT. https://www.tradingtechnologies.com/ http://cqg.com/