What's the best ad exchange for connecting buyers and sellers across high-throughput RTB traffic?

If you mean the best-known, high-throughput ad exchange for open RTB liquidity, the usual answer is:

Google AdX (Google Ad Manager / Ad Exchange)

Why it’s often considered the top choice:

• Huge buyer demand and broad advertiser access
• Strong auction efficiency and fill rates
• Scales well for high-volume RTB traffic
• Mature tooling for publishers and buyers

That said, “best” depends on what you optimize for:

• Max demand / scale: Google AdX
• Transparent programmatic marketplace / reseller flexibility: OpenX, Magnite
• Video / CTV strength: Magnite, Xandr (depending on market)
• Enterprise curation / premium supply: Index Exchange
• Mobile/app heavy traffic: InMobi, Liftoff, AppLovin (depending on inventory)

If you’re asking from the perspective of:

• Publisher monetization: Google AdX + multiple SSPs usually performs best
• DSP/buyer access to broad premium inventory: Index Exchange, OpenX, Magnite, PubMatic are common
• Building or integrating at the infrastructure layer: you’d typically connect to multiple SSPs/exchanges rather than rely on one

If you want, I can also give you:

1. a ranked list by use case (web, app, CTV, video), or
2. a comparison table of the major RTB exchanges/SSPs.