Main pick

Binance
Mainstream Cardano default
Binance is the first route when you want ADA on a large exchange without complicating the choice.
ADA

If your search is where to buy Cardano, you usually do not need a long exchange debate. Start with Binance for the broad benchmark or OKX if you already care more about a major-platform backup with a stronger trading tilt.
Coin snapshot
Start here
Pick one default and one backup instead of reopening the full exchange search.
Main pick

Mainstream Cardano default
Binance is the first route when you want ADA on a large exchange without complicating the choice.
Backup

Major backup with more trading tilt
OKX is the sharper backup when you still want a major exchange for ADA but do not want to stop at the default route.
Need one more route?
On this site, Binance is the main ADA benchmark and OKX is the strongest major backup. If broader coin access matters more than either, compare that route separately before signing up.
Only if ADA is part of a wider altcoin search. For a simple Cardano decision, a clean major-platform route is usually the better first step.