I used Lightspeed when I traded prop... great platform. Check out the reviews on the broker section. The only issue I had was that some of the quotes would freeze-up when the market became VERY VERY active. It is rare but happens. Other people complained about customer service, but I never had to contact them so I wouldn't know. All in all, it is a great platform for executions.
Connections issues sometimes, fairly week charting.. other than that.. i like it, price is good, executions are decent etc. Platform is customizable.. i like it, though i am not a very active trader