Hi BCV12,
Welcome to T2W.
There is no 'best platform' as such, just the platform that's best for you - which might be different to the one that's best for me or anyone else. That means you have to know what it is that you want. For example, if it's essential for you to be able to trade direct from charts, there's no point considering a platform that doesn't allow this. If it must have Point & Figure charts, then MT4 is not the platform for you. You get the idea. So, having compiled a list of essential and desirable features, it's a case of looking at all the likely candidates.
In tandem with this, I recommend you look at the services of the broker and, similarly, decide what requirements are essential and desirable of them. Are the tightest spreads all that matter to you, or are you prepared to compromise on that front for better service? Must they provide Negative Balance Protection to ensure you don't get caught out like a lot of traders did when the Swiss National Bank removed the peg that held the Swiss franc at a fixed exchange rate with the Euro in 2015. Again, you get the idea.
When you've done all of the above, you ought to be in a position to shortlist two or three. These days, all brokers will provide you with a demo account so that you can get to grips with their platform's features and functionality. They don't expect you to magically know how to use it before becoming a client and fund (and risk) real money before you know what you're doing. (NB: for clarity, I'm referring only to the platform and how to use it and not how to trade.) Brokers get a lot of stick from a lot of people - but they aren't that unreasonable!
It's worth taking your time doing all of this and getting it right. That said, most traders move about quite a lot for a host of different reasons and many have multiple accounts with different brokers. Some people will recommend giving MT4 a go - if only because most brokers offer it. So, if you like MT4 - that's the platform side of things sorted regardless of which broker you go with. However, it's geared towards Forex traders and not - as I suspect might be the case with you - equities traders. Also, it's pants, but that's just my own highly biased personal opinion.
Tim.