SIPA is a great program. The difference among Georgetown, SIPA, Fletcher, and SAIS is almost ignorable when you are job-hunting. You'll get your interview chances if you come out of any one of these schools, and it is up to you to rock it.
People say Georgetown and SAIS have geographical advantage but wouldn't the employer also consider a SIPA graduate if he/she is on the list of applicants?
The bottom line is, you go where you want to go. Certainly if it's WWS or KSG, there is a difference but not among Georgetown, SIPA, Fletcher, and SAIS.
Personally, although I hate SIPA's big class size, I will take SIPA over other schools because it's an Ivy. Sounds shallow but that's the reality. You'll be surprised how many people don't know SAIS and Fletcher .