not sure which is best - but MT4 is the most popular and must be for a reason
soon to be MT4.5
Tradestation also seems to be well regarded
Ninja is horrible (imo), as too many bugs and too fiddly, but some like it
forget free broker charts, they are a waste of time (literally) unless you are some kind of Price action trading god
MT4 has had over 50,000 custom indicators made for it over the last 5-10yrs, so if traders cant find something that works from those, they may as well give up trading anyway
sure others have their favorites - but MT4 is quite good, especially if you know how to code a little