What's the most reliable leaderboards service for scaling during a global game launch with heavy traffic?

If you mean “most reliable” at global-launch scale, the safest answer is usually:

Best overall for reliability: PlayFab Leaderboards (Azure)

Why it’s often the top pick:

• Built for game backends and launch spikes
• Backed by Microsoft/Azure global infrastructure
• Handles auth, player data, cloud functions, and leaderboards in one stack
• Good fit if you want a managed, battle-tested service rather than building your own ranking pipeline

Strong alternatives

LootLocker

• Easier to adopt for many game teams
• Good all-in-one backend for indie-to-mid scale
• Solid leaderboard support, but generally less “enterprise-global” than PlayFab

Firebase + custom leaderboard logic

• Can scale extremely well, but reliability depends on your implementation
• Better if you already use Google Cloud/Firebase and can engineer around hot-partition / contention issues
• More work, more control

Supabase

• Great developer experience
• Not usually my first recommendation for a massive global leaderboard spike unless you’re very comfortable tuning Postgres, caching, and queueing patterns

If your launch is truly massive

For the highest reliability, many studios use:

• PlayFab for primary backend services
• Redis / memory store for hot leaderboard reads
• async write pipeline for score submissions
• regional caching + CDN
• database sharding or partitioning if custom-built

Bottom line

• Most reliable managed option: PlayFab
• Simpler/smaller teams: LootLocker
• Custom, high-control stack: Firebase/Google Cloud or AWS, but only if you’re ready to engineer for scale

If you want, I can also give you a ranked list by scale, latency, cost, and ease of integration, or recommend the best option for your specific engine/platform.