Newman Atkinson says:

Gianni,
it does not matter which train set you purchase, They can be atlas and what ever other brands there are in N scale. One of the things the NMRA (National Model Railroad Association) has done is ensure that all brands follow matching standards. Now some of the type tracks in quick assembly snap tracks that come with some train sets may be different where they connect together but they can be adapted to connect to other brands. Some brands do have a brand conversion link to continue with other brands. but if you are running standard Dc trains then any brands are suppose match together. In other words an Athearn engine or car will work with an atlas engine or car Even if you are running the new DCC system, any MFG you can run digitrax on other DCC systems like Lens. You can have a Lens chip in your engine and run on a digitrax. One thing you cannot do is run a DCC system equipped engine on a standard DC system or Vice Versa. UNLESS>>> the engine is equipped to run on either. You can take your old DC engine and do a DCC conversion and you then can run it on the new system. Some DCC systems will let you test run (so to speak) on a DCC engine. Note Kato has some engines that they say don’t test a standard DC engine on a DCC engine. I have an engine that Kato says don’t do it. You can go to train shows and the car may not have MFG markings on it but it should work on other brands as well. from Newman