They want to go to University for IT Degree, but they heard that obtaining various IT Certificate is more useful than IT Degrees (Microsoft, Cisco, Novell, Linux etc).
I heard that a CCNA certificate just about garuantees you a job!

However those 'propriatary' courses are often much more difficult than say.. a diploma level course. I know, I did both within the same 2 years!

Which one is more flexible for the future?
A uni course is certainly more flexible, that's because it trains you in a much wider variety of subjects - it's kind of being a jack of all trades (but a really good 'jack')
Whereas those other courses are each much more specific.
If you do a networking one - you do it to learn networking only, ofcourse it's no good for programming, for example.
Which one will get a better job?
That's up to you.
You will have to work out what kind of job you want, and then get those skills, if you want to be a Sys. Admin. go for a more specific course.
The best thing to start doing is to browse through employment sites to see what skills people are currently after.
The best way to get a job in IT is to get
experience ! That ususlly means to look around places you might wish to work for and offer your services for free...
Chances are, that if you're any good they'll take you on.