best platform for automatic trading API

[MGB]

Consider www.NinjaTrader.com. Plenty of information on their website about their API.

Look under "Automated Trading".

http://www.ninjatrader-support.com/HelpGuideV6/helpguide.html

 

[Euler]

Sterling Trader Pro is also a decent platform with a good API -- it has a C++ API, but most of the example code is in VB, so that's what most people seem to be using.