TT seems to be the best product for professional traders and J-Trader seems to be the best product for traders just getting started. The real differentiator is cost vs. features between it and J-Trader. This is what I hear from Professional Prop traders and from customers that have used both.
J-Trader is usually billed as an add on per contract software product. It is just .50 per trade or something like that while TT is usually billed monthly. ($500.00) per month. This can be confusing. When you are doing more than 500 sides or 250 RT/month then J-Trader is about the same or less cost as TT. But, if you are doing 1000+ sides per month then the choice is obvious, you pay less for a high volume deal with TT as a monthly fee.
As for features, TT is preferred by most professional traders because it has many new features. You have easy to place stop loss orders and even the ability to drag and drop your orders on MD-Trader. You also get volume by price accumulation, X-Trader Pro auto spreader, and X-Trader auto traders. You can mouse trade or keyboard trade or even get an external programmable keyboard for news.
If you are starting out from scratch...and are going to do low volume, <200 trades per month, then J-Trader will probably be less expensive and easier to use. But if you start doing higher volume and want to switch to TT, you will have to learn a new software product.
Velocity Futures will let you try out (as members of elite trader) the TT product for a week or two for free using the simmulator. It is the same market data as is found on live product but with fake executions. You can goto our site and go through the open account procedure online (takes 5 minutes) then download the software and call us and we will set you up with a demo account for you to play on.
Check out both products out and decide for yourself.
http://www.velocityfutures.com/simulator_futures_trading.html
Jay