Anyone who suggests strategy developing in any of the mentioned platforms has never made an automated system more profitable than descretionary trading.
Strategy development takes place more in matlab, excel, braincel and many other non-trading platforms, including pencil and paper. People who try automated development solely in ___ platform are newbies on a yellow brick road trying to make a "grail" (automated system better than discretionary) out of traditional indicators (impossible).
I have tried Multicharts, SierraCharts, Lightspeed, eSignal, Ninjatrader, TWS, and a few others I can't recall. Since there seems to be a discrepancy with what a "amature" platform is (most likely due to the modest discretionary traders and nonprofitable ET dolts), I'll clearly define it for you - E*Trade is newbie, TWS web is newbie, Thinkorswim is newbie, Multicharts is a cross toward newbie. Almost all of the Java platforms are crap.
Ninjatrader is the best, with the big downfall of bugs. Charts in Ninjatrader are, at least imo, by far the most intuitive and easiest to work with. I can't imagine how many hours people must waste working with the mouse clicking/hand aching in the others. Automated trading (NOT development) is actually excellent in NT - I saw some other comments saying otherwise. Sorry, Mr. Discretionary

it seems allot of losers around here like to slam NT because they failed to come up with anything productive (read...profitable) in Ninja and ultimately left blaming the platform's downfalls instead of blaming themselves, even if 5%-9% of the problem was their responsibility to get around the NT bugs. My message to these shortcomers: pull your f*cking boot straps up and throw your pathetic of an ego out the door - stick with support and resistance until you decide to learn what really makes automated trading tick (hint: it doesn't involve any of the default 'indicators' you'll find in any platform!)
Be aware that there is allot of bias about Multicharts - anyone who is Russian will not only automatically proclaim it as number one, but will go borderline trolling against others when they say it's not. I think Ninjatrader is the clear winner in discretionary, however others are very good like Sierrachart and Lightspeed.
For automation, also check out Cyborg trading.
Bottom line.....not only does NT 7 outrank in discretionary trading, it still wins in automation and automated execution. Others don't cover this (lightspeed), don't cover it as well (Sierrachart), or do it in a very newbie and useless way with lots of feminine colors (Multicharts with easylanguage). Just my opinion, cheers.
edit: I know the OP was talking about 'professional', but I took it as professional retail. Real professional platforms would be none of the above. For institutional level, I recommend Bloomberg. But for a retailer, this may not be the best choice, even if bb is far superior to the rest. My $.02 is to look to Ninjatrader, considering it's UI, Ninjascript, and superior user following - but also try the trials of the other platforms. With Ninjatrader you can run a strategy that you would normally run in a custom app fabric while having all of the options that would be difficult in custom software or impossible in other retail platforms - multibroker (NOT available in ANY other platform - want one broker, mr corzine?), charts, detail pnl gen (couldn't even find this in TWS!).....