Well, you might have to ask a few more specific questions before we can help you..
First off, because NFOs are systems operators as much as aviators, the difference between one and another is huge... probably moreso than on the pilot side. An EA-6B ECMOs job doesn't have a whole lot in common with an E-2 bubba's. So any FO you talk to will give you a whole different shpiel... and by the same count, your career opportunities will vary accordingly.
So if you're Navy, you look at 4 different categories:
P-3s/EP-3s (and E-6s I suppose)
E-2s
EA-6Bs
F/A-18Fs
I also was wondering if anybody knew about a rumor I heard about getting #1 in API and being able to switch to pilot.
Yeah, that was true when I was going through... but I didn't really care in API all that much and didn't try

Bottom line is that most folks when they get out to flight training end up being happy with being 'FOs anyways
As far as career opportunities... well, I mean... other than being an airline pilot, I don't know that being an SNA is any better. And being one of the 50% who goes helos won't exactly deliver you to the Delta 777 captain's chair either.
Bottom line is that being a military officer in the first place will carry weight in the civilian sector. Being the mission commander of a multimillion dollar aircraft that carries lots of things that go boom will also carry weight. And if you really want to worry about your life after the military, there's opportunities to get your postgraduate degree on your shore tour.
I would also recommend the 'Summary of NFO flight school' post that's rolling around here... it's quite comprehensive, though remember it'll only apply to Prowler bubbas...