Before you confirm a swap you are asked to choose a rate type. Most people pick whichever number is bigger and move on. That choice decides who carries the risk of the market moving while your coins are still in transit, and it is worth ten seconds of thought.
What a floating rate actually means
A floating rate is an estimate. The amount shown is what you would receive if the market stayed exactly where it is until your deposit confirms. It will not. Between the moment you click and the moment the network confirms your transaction, the price moves, and the amount you receive moves with it.
You benefit if the pair moves your way, and you receive less if it moves against you. Nobody is charging you for that risk, which is why the headline number on a floating rate is almost always better.
What a fixed rate actually means
A fixed rate locks the amount at the moment you create the swap. Whatever happens to the market during confirmation, you receive the number you were shown.
That guarantee is not free. The provider is taking the market risk you did not want, so the rate is a little worse than the floating equivalent. The gap is the price of certainty, and it is usually small.
A fixed rate also comes with a deadline. You have a limited window to send your deposit, because the lock cannot be held open forever. Miss it and the swap expires and is refunded.
The question that actually decides it
Forget which number is larger. Ask instead: how quickly can I send the deposit, and how certain am I of that?
If your coins are in a hot wallet on your phone and you will send them in the next two minutes, a fixed rate gives you certainty at almost no cost, because there is barely any window for the market to move.
If you are moving coins out of cold storage, signing on a hardware wallet, or sending a coin with slow confirmations, a floating rate is usually the saner choice. A fixed rate you cannot fund in time is worse than no lock at all: the swap expires, the funds go back, and you start over.
Volatility matters more than the pair
The more volatile the coins involved, the more a fixed rate is worth. Swapping a stablecoin into another stablecoin barely moves during confirmation, so the lock buys you almost nothing. Swapping a volatile asset into Monero during a fast-moving hour is exactly when the lock earns its keep.
A practical rule
Fixed rate when you can fund immediately and the pair is volatile. Floating rate when funding will take a while, when confirmations are slow, or when both sides are stable. If you are unsure and the amount matters to you, take the fixed rate: paying a little for a known outcome is rarely the decision you regret.