When deciding between abstract classes and interfaces in practical software development, it's essential to understand their differences and use cases. Here’s a comprehensive breakdown to help make the right choice:

Abstract Classes

Definition:
Abstract classes are classes that cannot be instantiated on their own and are meant to be subclassed. They can have method implementations (concrete methods) as well as abstract methods that need to be implemented by subclasses.

Key Features:

1. Method Implementations: Abstract classes can include both abstract methods (without implementation) and concrete methods (with implementation).

2. Constructors and Member Variables: They can have constructors and member variables, which can be fully utilized in their member methods.

3. Access Modifiers: Abstract classes support access modifiers like private, protected, and public for their methods and fields, providing a rich encapsulation model.

4. Inheritance: A class can extend only one abstract class, fostering a closer relationship between abstract classes and subclasses.

Use Cases:

• When you have closely related objects with shared code.
• When base class contains some default behavior that should be inherited by all subclasses.
• When you need to use fields or methods with access modifiers for encapsulation.

Interfaces

Definition:
Interfaces are contracts that define a set of methods but do not provide implementations. Classes that implement an interface must provide concrete implementations for all its methods.

Key Features:

1. No Method Implementations: Interfaces can only declare methods without providing bodies, although Java 8 and newer versions allow default methods with implementations.

2. No Constructors or State: Interfaces can't hold state with instance variables or have constructors.

3. Multiple Inheritance: A class can implement multiple interfaces, which is useful for integrating multiple behaviors without the constraints of single class inheritance.

4. Functional Design: Especially useful for defining capabilities or behaviors that can be shared across different class hierarchies.

Use Cases:

• When you need to specify that a class must implement certain methods but do not want to dictate how.
• When multiple inheritance is required for classes to inherit behaviors from different sources.
• Designing plug-ins or modules that need to comply with a fixed contract but are independent in terms of implementation.

Making the Right Choice

1. Consider Code Reuse: Opt for abstract classes when there are common methods across classes that could use shared code.

2. Design for Flexibility: Use interfaces when you need to provide a flexible design that can work across disparate class hierarchies and allow multiple inheritance of behaviors.

3. Inheritance vs Composition: Use abstract classes for a "is-a" relationship and interfaces for an "implements-a" capability.

4. Change and Evolution: Abstract classes are more suitable for evolution over time if you expect them to change frequently with additional shared behavior, while interfaces offer stability and are often best used when the contract remains constant.

5. Language Considerations: Remember that languages like Java with interface default methods blur the traditional lines significantly, so consider language capabilities when making your choice.

Ultimately, the decision should be guided by the design needs, future maintenance considerations, and specific language capabilities of your project. Balancing these factors will help you choose between abstract classes and interfaces effectively.