“Best” depends on what you value (speed, punctuality, scenery, luxury, overnight comfort, frequency). Below is a compact, curated list of standout train services worldwide grouped by what they’re best at, with a one-line note for each and quick suggestions.

Top high‑speed & long‑distance passenger services

• Japan — Shinkansen (JR): world-class punctuality, frequency, safety and comfort across multiple lines (e.g., Tokaido, Sanyo). Great for intercity business and sightseeing.
• France — TGV (SNCF): very fast Paris↔regional connections and excellent onboard service.
• China — China Railway High-speed (CRH/CR): largest high‑speed network, extremely fast and frequent on major corridors.
• Spain — AVE (Renfe): fast, comfortable connections (Madrid–Barcelona, etc.) with good service levels.
• Germany — ICE (Deutsche Bahn): reliable high‑speed regional backbone across Germany and into neighboring countries.
• South Korea — KTX: modern, punctual high‑speed service linking Seoul with major cities.
• Russia — Sapsan: fast St. Petersburg ↔ Moscow service (if you want a high‑speed option across Russia).
• UK↔Europe — Eurostar: high‑speed cross‑Channel link London ↔ Paris/Brussels/Amsterdam.

Best scenic & experiential routes

• Switzerland — Glacier Express / Bernina Express (Rhaetian Railway): dramatic Alpine scenery, panoramic cars, top scenic experience.
• Norway — Bergen Line: spectacular fjords and mountain landscapes.
• Canada — Rocky Mountaineer: luxury daytime-only routes through the Canadian Rockies (Vancouver–Banff/Jasper).
• India — Darjeeling Himalayan Railway (toy train) and mountain routes (scenic narrow-gauge experiences).
• New Zealand — Northern Explorer & TranzAlpine: rugged landscapes and coastal/mountain scenery.

Top overnight & sleeper trains

• Austria/Germany/Europe — ÖBB Nightjet: modern sleeper network across many European cities; growing and reliable.
• UK — Caledonian Sleeper: overnight between London and Scotland (sleeper cabins).
• Australia — The Ghan (Adelaide–Darwin) and Indian Pacific (Sydney–Perth): epic long-distance journeys with dining and off‑train excursions.
• Russia/Trans‑Siberian — Private luxury operators (e.g., Golden Eagle) or classic Russian sleepers for the full Trans‑Siberian experience.
• South Africa — Blue Train: very high-end, luxurious overnight service (Cape Town ↔ Pretoria).

Luxury & heritage trains

• Venice Simplon‑Orient‑Express (VSOE): famous vintage luxury across European routes.
• Maharajas’ Express (India): ultra‑luxury palace‑style train for heritage tours.
• Belmond trains (e.g., Belmond Royal Scotsman): luxury experiences focused on service and scenery.

Urban & commuter systems noted for quality

• Japan (Tokyo area rail + Shinkansen feeder services): unsurpassed frequency, cleanliness and on‑time performance.
• Switzerland (SBB): exceptional punctuality, integration and scenic local/intercity services.
• Singapore, Hong Kong, Seoul metro/rail networks: extremely clean, efficient urban networks.

Practical recommendations (short)

• If you want speed and business travel: Shinkansen, TGV, ICE, KTX, China HSR.
• If you want scenery/daytime luxury: Rocky Mountaineer, Glacier Express, Bernina Express.
• If you want an iconic overnight: The Ghan, Indian Pacific, ÖBB Nightjet, Trans‑Siberian.
• If you want vintage luxury/experience: VSOE, Maharajas’ Express, Blue Train.
• For frequent, reliable commuter travel: Japanese and Swiss rail systems.

Booking & travel tips

• Book early for popular scenic and luxury trains; sleepers and panoramic seats sell out.
• For multiple countries in Europe consider rail passes (Eurail/Interrail) but check seat‑reservation fees on high‑speed and night trains.
• Overnight sleepers: compare couchettes vs private cabins vs first‑class sleepers for comfort and price.
• Check border/ID rules when crossing countries (Schengen vs non‑Schengen) — carry passports.
• For high‑speed trains: arrive 10–20 minutes early; for luxury trains arrive earlier for boarding rituals and briefings.
• Look at class/seat types (business/green/first) — sometimes the price jump is worth the extra space and meal service.

If you want, I can:

• Narrow this to the “top 10” by a specific criterion (speed, scenery, luxury, family‑friendly), or
• Give route examples, fares and booking tips for a particular country or trip you have in mind.

Which criterion or region should I focus on next?