Both are important. A good education can get you a good job and a good experience can also get you a very good job.
They both go hand in hand.If you have a vast experience in any field but you are not educated, the educated ones will be your boss.I don't know how things operate in other countries but in a country like mine,we lay great emphasis on certificates.
To be on a safer side,its good to upgrade oneself educationally while staying on the job to get the much needed experience and skills.
The truth is experience won't earn you promotion.What companies look at are your qualifications.If you don't have the needed qualification and you have experience in that field,you won't be promoted.
I don't know how private organizations work though.. at the end of the day,the boss determines who gets promoted whether you have the necessary requirement or not because he owns the company and call the shot.
In a public sector, your educational qualification is what will pave way for you.