What's the best private marketplace for buying premium placements?

The “best” private marketplace depends on what you mean by premium placements and your goal:

If you mean programmatic ad inventory

The strongest options are usually:

• Google AdX / Google Authorized Buyers — widest reach, especially for premium display/video.
• OpenX Private Marketplace (PMP) — good premium publisher access.
• Magnite — strong for video/CTV and premium publishers.
• Index Exchange — often praised for quality supply and transparency.
• PubMatic — solid premium inventory and curation options.
• Xandr (Microsoft) — enterprise-friendly, especially for larger buyers.

If you mean private marketplace for domains/names/usernames/social handles

Then “premium placements” could mean a totally different thing, and the best marketplace would vary a lot by asset type.

Best general rule

If your goal is high-quality, brand-safe inventory, start with:

1. Google AdX/Authorized Buyers
2. Index Exchange
3. Magnite
4. OpenX PMPs
5. PubMatic

What to choose based on your needs

• Best reach: Google AdX
• Best premium video/CTV: Magnite
• Best supply quality/transparency: Index Exchange
• Best for curated PMPs: OpenX / PubMatic

If you want, I can narrow it down based on:

• display vs video vs CTV
• budget
• geography
• brand safety needs
• self-serve vs managed service