Both approaches can be considered RESTful, provided you do not break the REST constraints defined in the chapter 5 of Roy Thomas Fielding’s dissertation:
- Client-server
- Stateless
- Cache
- Uniform interface
- Layered system
- Code-on-demand
I cannot see major pitfalls in both approaches, but I would prefer the Approach B over the Approach A: the URLs are shorter, easier to remember and not many parameters are required.
Bonus points: Spotify and Facebook APIs follow this approach. For sure there are other APIs, but these are the ones that came up to my mind.