My God, never expected you guys to be here. Now I have to raise the bar.
Anyway, to start off, here are some basic assumptions (particularly for newbies):
1. You already know about trading
2. You are well capitalised to justify the software costs
3. You have zeroed in on your trading philosophy and know what you are looking for (in trading, not software).
I will keep my personal biases away and try to put as much stuff as possible here. So lets start.
Remember all software are not made equal. Other than the basic, intermediate and advanced usage, there are software that claim to do many things, but are good at only a few things. So first write a statement as to what you want to do with the software that you plan to purchase/use.
Some valid points may be:
1. I want to view market profile
2. I want to create custom indicators
3. I do not want to view indicators but need signals to trade
4. I want to scan >5000 symbols every 5 minutes
5. I want to look for chart patterns to trade
6. I want to create robust statistical techniques
7. I want to create option strategies - plain vanilla to exotic
8. I want to do intermarket analysis
etc etc.
Now go back and add another column and put real/time or end of day next to all your statements.
Once done you are ready to delve deeper.
The first thing we ask is cost. This is not correct. First ask, is it the right stuff for me (Will come to "right stuff" later). If yes then only go for cost. Cost is not just the software cost, but the hardware and the data service to run it properly. Also consider upgrades.
More later.