There are a few reasons why we prefer Dictionary over Hashtable in C#:

• Type safety:Dictionary is a strongly typed collection, which means that the type of the key and value must be specified when the Dictionary is created. This prevents errors from occurring when you try to add or retrieve elements from the Dictionary. Hashtable is a weakly typed collection, which means that the type of the key and value can be anything. This can lead to errors if you try to add or retrieve elements of the wrong type.
• Performance:Dictionary is generally faster than Hashtable because it does not require boxing and unboxing of the keys and values. Boxing and unboxing is a process that converts value types to reference types and vice versa. This can be a performance bottleneck, especially when you are working with large collections.
• Features:Dictionary provides a number of features that Hashtable does not, such as the ability to iterate over the keys and values in a specific order, and the ability to check if a key exists in the Dictionary without actually retrieving the value.

In general, you should use Dictionary instead of Hashtable unless you have a specific reason to use Hashtable.

Here is a table that summarizes the key differences between Dictionary and Hashtable: