Since i am using a 1.6xLF DSLR, I would say the serve different purpose. hence, it all depence what's the subject and what kind of effect you want in your pic. Anyway, I own both because to me, they compliment each other well.
or it looks very bad, because of improper use. a lot of people end up just shooting ultrawide without proper composition, end up with photos with too much space, or photos which are messy due to the huge amount of elements you need to include in your frame.