The two markets behave differently enough that the answer is rarely "either".
Where Japanese cards win
- Print quality and centring are noticeably more consistent, which matters enormously if you grade. A far higher share of Japanese cards come back as 10s.
- Cost per pack is usually lower, with higher pull rates on many sets.
- Card stock is stiffer and tends to survive handling better.
Where English cards win
- Resale liquidity in the UK, US and EU. A far larger pool of buyers means faster sales and tighter spreads.
- Recognition. For a collection you intend to sell to a general audience, English is simply easier to move.
- Set structure familiarity — English sets map to what most Western guides and checklists describe.
The practical answer
Many collectors do both, deliberately: Japanese for cards they intend to grade or keep, English for cards they intend to trade or sell on. If you collect for the art and the chase, Japanese sets are excellent value. If you collect with one eye on resale in the West, English is the safer default.
Tracking both
Japanese sets are catalogued here alongside English ones, with their own pricing — browse the Japanese Pokémon sets free. Note that pricing on Japanese cards comes from a different source than English base prints, and coverage differs; the specifics are documented on the price data page.