I have found that many brokers will allow you to demo their trading platform.
Most offer 14 days. Some offer more.
Here is a list of brokers that I have found that offer free platform trials.
Keep in mind that there are many more.
NINJA BROKERAGE (Talked to a rep there, that had a lot of trading experience and was very cool. (RICH) ATC BROKERS (My current broker and also low pressure real nice sales team. (ROBERT) CANNON TRADING (Lots of platforms available, These guys have been around a long time.)JOE) THINK OR SWIM (Ameritrade. Download platform from think or swim. Tons of tools, news and access to equities) GO FUTURES (Don't know much about them but they do have good basic tutorials on their website for the begginner) DECARLEY TRADING (THese nice ladies will also send you their trading thoughts to your email....which is nice!) NADEX (Binary options which I know little about, but they offer a free trial)
These are just a few off of the top of my head.
THere are many more.
Can't really say who is best, I'm still trying to figure out what is best for me.
Also search threads on this site for key words regarding brokers and platforms.
Lots of good info here.