Make your way to the following thread to get input on the offshore side of the question. Highly active.
On the US broker side, I honestly think you’ll need to just jump in and get your feet wet. Don’t forget trading.com, a new entrant into the US market. I believe IBKR also offers forex trading accounts, but not sure if that includes retail or not.
GAIN is the largest by market share, followed by OANDA, if that matters to you.