I use either paper towels and alcohol, or the brass wire brush.
If you choose to go the brass wire brush route, look at using the Trix wheel cleaner brushes instead. They come as a block 4 inches (or so) long that you set onto the track. They can be ganged end-to-end, which allows you to clean all of the drive wheels on even the largest steam locomotives. They're a lot less fiddly to work with than the little Kadee hand-held job.
The Trix one is their item #66602. The photo that Walthers shows on their site is an earlier design of the same item number. At $33 and change, they've gone up over 50% in price since I bought mine at $20 apiece a number of years back.
In all the years I've been using these, I haven't seen any plating wear that I could attribute to the wheel cleaner.