Q:

What type of microphone is best suited for recording ambient sounds? 

I've seen countless examples of recordings of an environment that are supposed to help you fall asleep. 
Examples: Train ride or Heavy Thunderstorm
I am wondering, what is the best kind of microphone to record such things? 
It should capture all of its surroundings as they are to give the listener the illusion they'd be right there.  This especially means that it should be capable of recording surround audio.  By this I mean that sounds that are right to the microphone should also appear on the right audio channel in the output file.  Respectively for the other directions. 
I have no experience in audio design.  So please be kind to me. 
I am not asking for a specific microphone, but rather for a specific type of microphone I should be buying. 

A:

Since you need natural sounding stereophonic sound, you would need two cardioid mics set up as a near coincident pair.  
There are actually two ways of doing this, the French (ORTF) and the Dutch (NOS).  
They both provide wide stereo image which I think will make the recording more interesting and atmospheric. 
As far as using a dynamic or condenser set of mics, this will depend on the material as well as the conditions.  Condenser mics have wider frequency response but are also more sensitive and this could prove to be a problem when it's windy for example.  They also need phantom power (+48V) to operate and this could be a problem for field recordings unless you have the right equipment.  
Dynamic microphones on the other hand are less sensitive but have a narrower frequency response than condenser.  
My first preference would be a set of condenser mics, as long as I'm not expecting a windy day or an environment with high vibrations - although a proper mount would probably solve the latter.