Both are popular sizes, but they serve different purposes. Here's how to decide which one to buy.
5ml Decant
Sprays: ~50 sprays. Duration: 3-4 weeks of daily wear (2 sprays/day). Price: $3-8 depending on the fragrance. Best for: Testing a fragrance before buying a full bottle, travel, building a varied collection on a budget, or trying something you're curious about but not sure you'll love.
10ml Decant
Sprays: ~100 sprays. Duration: 7-8 weeks of daily wear. Price: $6-14. Best for: Fragrances you already know you enjoy, extended travel (2+ weeks), a semi-permanent rotation piece, or when you want more than a trial but less than a full bottle commitment.
The Decision Framework
Never tried it? Go 5ml. You'll have enough to test it across multiple days, weather conditions, and settings. If you love it, you can upgrade.
Already tried it and liked it? Go 10ml. You get double the wear time at less than double the price (better per-ml value).
Planning to buy the full bottle anyway? Go 5ml as a bridge. Once the decant runs out, you'll know for certain the full bottle is worth it.