I was asking myself the same question lately because there seem to be quite a few options these days.
I think it depends on your use case and also your coding style. Some gems handle serialization in the view layer (e.g. Jbuilder, Rabl, etc.) and others in the model layer (ActiveModel::Serializers, JSONAPI::Resources, Roar.).
JSONAPI::Resources is great if you plan to stick with the JSON:API spec, but can also feel a bit heavy-handed (you have to incorporate its helper methods into your routes, controllers, and models).
I summarized the different options in a recent blog post that you might find helpful.
Check it out here: Which JSON Serializer To Use For A New Rails API?