JackofWands
I agree with the RWS/Thoth/Marseilles combo. Even if your friend is looking to start reading, rather than just collecting, the Marseilles and Thoth decks can provide good next-step challenges for intermediary and advanced readers.
After that, I would say one deck in the RWS tradition but with non-traditional artwork (e.g. Light Visions, Shadowscapes), and, as RiverRunsDeep suggested, a "themed" deck.
After that, I would say one deck in the RWS tradition but with non-traditional artwork (e.g. Light Visions, Shadowscapes), and, as RiverRunsDeep suggested, a "themed" deck.