Marketiva is growing very fast.
Check on the page
"With more than 210,000 serviced users, 120,000 unique and live trading accounts, and more than 2.4 million live orders executed each month, Marketiva is one of the most popular over-the-counter market makers in the world."
Its currently my broker and im very happy with them. And to try them the free $5 is a big bonus.