Here's a comparison:
Fixed Dumbbells: These come in a set weight and are more durable, generally providing a smoother and more balanced feel during exercises. However, they require more space and can be costlier if you need a wide range of weight options.
Adjustable Weight Dumbbells: These allow you to change the weight by adding or removing weight plates. They are more compact, cost-effective (as you can adjust a single pair for multiple exercises), and require less storage space. However, they may have a bulkier design and may take slightly longer to adjust between weights.