Uniqueness 
It’s difficult to find a nice balance between a name that is unique but doesn't appear to be too weird.  Having an unusual name has the advantage of making you stand out from the crowd. However, a name no one has heard of or can't pronounce can bring embarrassment and unwanted attention to a child.  Common names that are easily recognized and easy to spell will cause your child less problems in the schoolyard in early years.  If the name is all too popular your child may find himself one of several “Johns” in the classroom.  this can be confusing and frustrating for the children and the teacher. Having a unique name, however, may make your child stand out and feel extra special.  One way of finding a compromise is to choose a familiar first name if the child's surname is unusual, and vice versa. If your son's surname will be Jones, you will want to consider something more unusual than Jack for his first name. However if his surname is Friedensteinkopf then Jack might be preferable to, say, Archibald, as a first name. 

Spelling and Pronunciation 
Unique names are often difficult to spell or pronounce because people haven’t heard them before.  It’s an important factor to consider.  If it’s a name that is hard to pronounce it would probably also be difficult to spell.  In the same way, creative spellings or pronunciations of popular names will cause your child no end to the task of correcting people that make mistakes in spelling or pronouncing their name.  An extra task they would rather do without, and you will get the blame for it.
Unusual spellings will also mean you have to special order or do without the personalized items that are sold in many shops.