Open-celled spray-in foam insulation is by far superior to a traditional radiant barrier which is a foil-like thing that you can either tack to the rafters or lay on the floor of your attic.
Open-cell foam is also more expensive, but in my opinion an excellent investment.
Radiant barrier works in conjunction with your blown-in insulation and is better than having blown in insulation only. Radiant barrier tacked to the rafters is superior to radiant barrier laid on the attic floor. Radiant barrier laid on the attic floor is better than painted on radiant barrier.
Blown in insulation alone is better than nothing.
If you have no insulation it is better than living with your mother in law, which is better than living under an interstate overpass, but only marginally.
Note - if your HVAC system is located in your attic, the best way you can go is with the open-cell spray-in foam insulation.
I have to give this project 5 hammers though because you shouldn't, no, you can't install spray-in foam yourself.