realistic ATC

I use VoxATC. It's voice recognition software that avoids having to use the ATC menu at all. A little unusual to get used to but there are settings to reduce the accuracy of your response to get ATC to respond. In fact it can be set really low so ATC will accept anything you say.

It has all the basic comms with ATC including declaring an emergency or requesting alternative runways, airports etc and works with FS flight plans. The documentation contains an example VFR and IFR flight with a full script of each demo flight.

There is a prompt screen that will show you what to say but it can be switched off once you get used to the sequence and content of communications with ATC.

Currently the ATC voice is the Microsoft SAM voice but it's not too bad. It is also standalone software that interfaces to FS so you have to have the default ATC switched off. You can hear other aircraft in your locality but it is not the AI aircraft you see in FS. Apparently the developers are working on interfacing with the FS traffic.

It's payware but actually talking to ATC instead of pressing buttons to select a response is far more realistic. They have a 30 day restricted demo download.

Their site is www.voxatc.com

A great one to use is www.vatsim.net.

That's about as real as you can get, where the controllers all fully trained, real world SIDs STARs and approaches are musts, voice and text can be used, and all interactions are fully responsive! (depending on the controller logged in at the time ).

The only downside is you aren't always flying through controlled airspace, so you have to pick your flights based on that (or just fly with the same careful attention to clearances and flights just on UNICOM). You also sacrifice using AI aircraft during the session (although now you gain human-intelligence-aircraft!). I've heard of people integrating both, but usually not successfully.