Dcc

As Nigel says, that's not a question anyone can give you a definitive answer to! However there are a few pointers in the right direction:

Buy a European system.

Buy a systen that enables you to read and program CVs in a straightforward manner.

If you intend running sound, make sure your controller allows you to set functions keys to either latching OR push to make.

Think about how important wireless control will be to you.

Think about whether you might prefer touch screen control for a throttle or a physical knob.

Watch as many YouTube videos as you can of how different systems are used. You'll find videos posted for most of them.

Then, once you done all your research and worked out what's best for you go out and buy a Z21.

Well there seem to be about 3 favourite systems of which I used Roco Z21, the above advice is sound I went this way because
1. I have a lot of locos
2. The use of an ipad or android keeps the cost down but once you get beyond 100 locos you need to ensure you have lots of capacity, Roco tell me I can run more ipads etc. on the system which will help now I am over 200 locos.
3. These devices give superior graphics
4. The white box version is cheaper still than the black box version.
5. DCC can be slow so ensure it does what you want
6. The advice above is good which leaves you wondering which way to go, I liked the ECOS before I bought the Roco Z21 and there are other good systems
7. Other benefit of the Roco is that it works with the modules such as the reverse loop etc found in Flieschman and Roco systems.

So there you have it, a lot of options, I'll suggest to others reading that they also post their system and give some idea if any good at all.

Kris.