Scenery File Placement

I am a little surprised that no one has jumped in to try to answer this, but it is probably because there may not be a good answer. I do not have any of the addons that you mention, so I can't give you a definitive answer, but perhaps I can give you some things to look for that might help you make that decision.

The airport definition files describe characteristics of the airport. For the sake of this discussion I'll separate them into two categories. First there are things that describe the visible aspects of the airport: runways, taxiways aprons, buildings, etc. The second category is the definition of the aircraft parking spots: location, size, parking codes, etc.

If there is detailed airport scenery in your other addons, and they have provided their own airport definition files, then the visible elements defined in those aircraft definition files probably have been customized to match the other scenery elements provided by the addon scenery. It is likely that the airport definition files provided by TrafficX will have visible elements that are closer to the default airports and therefore may not match the other scenery elements provided by your addon scenery. So in this case it would be preferable to have the TrafficX airport definition files at a lower priority in the scenery library than your addons. However, if the other addons contain airport definition files, their parking spots may not have the correct radii or parking codes to match the TrafficX aircraft, and there may not be enough parking spots to handle the volume of AI traffic that TrafficX provides.

So, if you wanted to take the easy way out you could first try putting the TrafficX airport definition files higher in the list than your addon scenery and see if that creates any visual problems. If it does, then try putting the TrafficX airport files at a lower priority. Then try to see if you have a reasonable amount of AI traffic.

But if you want to do a little more work, you can get a better idea of which order they should be in by examining the aircraft definition files. You can do this nicely with the free ADE or the payware AFX.   I use AFX, but ADE works very well and the price is right.

With AFX (and I assume ADE as well), You can search for all of the airport definition files for a given airport. When you open each file you can see all of its properties, including the folder in which it resides. So if an addon scenery provides an airport definition file, you should see three files listed, the addon, the TrafficX file and the stock file. By looking at the 3 files you can get an idea of how they differ. You can see if the addon file contains enough parking of the right size and with the right parking codes, etc. That should help you decide the relative priorities.

Having said all that, here is what I do. I have my TrafficX airport definition files at a higher priority than the stock airports, but at a lower priority than any addon scenery. If I add some addon scenery that contains an airport definition file, I examine that file (with AFX) to see if it contains adequate parking for the AI traffic that TrafficX (and my other AI traffic packages) provide. If changes need to be made then I start with the addon scenery airport definition file and modify it to enhance the parking layout. I save the resulting file in a separate folder that I add to the scenery library at the highest priority.   I may also remove the TrafficX airport definition from the environment (by renaming the extension to something other than .bgl) so that it doesn't get in the way.

And I guess I should add that all of what I said above assumes that the addon scenery provides airport definition files. If it does not, then I don't think it should matter where in the scenery library you put the TrafficX airport files, as long as they are at a higher priority than the stock files.