Do you prefer to work on the front end or back end of a product? What are the pros and cons of working on Front end and back end ? Front End: problems

Do you prefer to work on the front end or back end of a product? What are the pros and cons of working on Front end and back end ?
Front End: problems include similar to user interface design. its importance is very high for end user.
Back End: based on requirements, back-end of the system should be performance oriented and more scalable. sometimes more challenging with customer problems to change the design of back-end.
bottomline: Both front-end and back-end have specific requirements and challenges. Based on my experience i prefer to go with back-end. i would like to see myself involved more in the way the data is stored or retrieved with focus on performance and scalability. Of course both of these need to be tested well; either automated or manual testing or mix.