Short answer — there are three categories of platforms people most often use, and within each category a few widely used examples:

1. Airline / alliance websites (most reliable)

• Examples: United.com, Delta.com, American Airlines (AAdvantage), AlaskaAir.com, BritishAirways.com, AerLingus/Qantas sites.
• Why: They show the carrier’s own award inventory and are required for booking many partner awards and for using miles deposited with that airline.

2. Award-search aggregators / specialist tools (faster, often find partner space)

• Widely used: Point.Me (formerly Juicy Miles), ExpertFlyer (search + alerts, subscription), AwardLogic/award-focused search engines.
• Why: They search multiple programs and partners, surface good routing/partner-availability options, and can save time vs checking many airline sites manually. Most are paid or have premium features.

3. Tools for tracking, transfers, and booking help

• Examples: AwardWallet (track balances/expirations), airline credit-card portals, and paid booking services that will book award tickets for a fee.
• Why: Helpful for managing balances, getting alerts when space appears, or having an expert book complex partner awards for you.

Practical tips

• Start with the airline that holds your miles (or its alliance partner) because that’s where you’ll book. Then use an aggregator to find partner availability faster.
• Remember NOT all aggregators show everything — sometimes you must search the operating carrier’s site (or call) to see/book partner inventory.
• Verify fees, routing rules, and transatlantic/stopover rules on the airline where you’ll ultimately ticket the award.
• Consider paid tools if you search awards frequently — they often pay for themselves in time saved and better availability discovered.

If you want, tell me which frequent‑flyer program(s) or route(s) you care about and I’ll recommend which specific sites/tools to check first.