There is no such thing as "best" forex broker, really. Every single one of them has advantages and disadvantages. What really counts are your preferences when it comes to forex broker. What is important to you? What is your trading experience? What is your budget? etc.
If you have some money to invest, I suggest ActivTrades or FXCM. If you are looking for trading with $1-$10 then go with either InstaForex or Liteforex...
As I said, it is really up to you.
Also, the best way to check if the broker "suits" your needs is to open a demo account and see it for youself. Check the customer support - the willingness to help and the speed of response.
Here is another thing to consider - what is your payment method? Do you want to use your credit card? Or Paypal? Or Moneybookers? Not all brokers accept all the available payment methods.
If paypal is your primary payment method - I would suggest going for Avafx.
There... lots of choices, so little time! LOL!
