All RealTick brokers are the same if you are trading from a retail account. However, if you are trading for a fund/institution, look beyond the interface and towards how well your rep knows the software and the people at Townsend. You may also look to see if the broker offers a back-up system, access to syndicate deals, free API development and desk trading. Also, ask for a flat, per-share, all-in fee.
The software is the same. Other charge may vary. Route are not the same, depends on the broker. Some like Terra & Mastertrader provide free educational service.
RML trading is another one to look into. Rob Luecke (the owner) is a trader. I know his firm has been around for at least 5 years.