How to choose between a fixed and floating rate?

The choice depends on what matters more to you: predictability or a market-based rate at execution. If you want to know the exact payout upfront, choose a fixed rate — the amount is locked in the order. With a floating rate, the final payout is calculated using the current market rate when the order is processed, so it may change: if the rate moves in your favor, the amount shown when the order was created will not increase, and if the rate moves against you, the payout may be recalculated at the current rate.