Present Cont. - used when talking about future planned actions, E.g. I'm flying to Madrid tomorrow (you've already booked a ticket, arranged meeting there and so on)
Future Simple (will) - the most common usages:
- decisions taken at the moment of speaking
- speaker's determination, e.g. I will finish it no matter happens.
- predictions, assumptions, fears, hopes, speculations
- future habitual situations
- in conditional Type 1
- formal announcement, weather forecast
Present Simple - used when sth comes out of a schedule, TV programme, calendar etc. e.g. The train leaves at 5 o'clock.
Be going to - used either to show intention or when we are assume something is going to happen, for example Look at those clouds! It's going to rain.