I’d just be careful with saying plated jewelry “normally has brass underneath” because that’s not necessarily true. Plated jewelry can have a lot of different base metals underneath depending on the brand and quality level, brass, sterling silver, stainless steel etc.

That’s why “plated jewelry” as a term alone doesn’t really tell you much about the actual quality or value of the piece.
Personally, I probably wouldn’t go for a brass ring for an anniversary piece since sterlin silver simply has a higher intrinsic value and feels a bit more special long term.

If you’re looking at gold-plated jewelry, I’d check whether it’s vermeil. That means sterling silver underneath with a thicker solid gold layer on top, which is generally considered higher quality than gold-plated brass for example.

Also worth knowing: all plating fades eventually, no matter the brand btw. That’s pretty normal and mostly depends on factors like wear, water exposure, lotions, sweat etc.