If you are looking to invest in stocks then you certainly will require the services of a stockbroker. Stockbrokers have the license to buy and/or sell shares on behalf of investors. Considering the notorious roles stockbroking firms played in crashing the stock market in 2008, it becomes important that one deals with firms that have the capacity to deal in high volume and value trades. However, that is not to say smaller firms are not equally good, after all for an investor attention and customer service is as important and corporate governance. Smaller firms give smaller investor attention and peer to peer advice which may be difficult to get from the big 10.
Here they are, first by volume of trade and next by value of trade for the first 5 months. For more check here