Which dcc.

Whatever control system you go with look at Zimo decoders first. They are £20 each regardless of socket and you will not get anything better for the money, and anything cheaper will be of lesser quality.

As was stated above, fit a socket if there is none in the loco (I prefer PluX sockets such as the Zimo ADAPLU sockets since it is easy to upgrade lighting and sound later if you want to - other sockets have less function connections and a more limited range of decoders that fit).

You really need to know what you want from your control system before anyone can recommend one, there is no universal 'best' system, just best for doing certain things.

A £40 Lenz Gold is nearly as good as a £20 Zimo. The only thing that Lenz has that Zimo has not is the jst-9 socket option, otherwise I would have changed all my Lenz decoders for Zimo by now. The Lenz decoders do usually need some configuration to get good performance, but they can be made to work.

I have four ESU decoders, three with sound, and I am sure one day I will be able to get basic adequate performance out of at least one of them - until then I will just tear my hair out every time I try and use them.

The Zimos all just work out of the box without any need for configuration, they make life so much less stressful.