Depends.
The moulded ones can be worse than the foam ones. To be sure you'd have to do a leak test. Some brands offer them for free and redo them if they leak.

The big benefit of the moulded ones are the filters you can have put in. These filter out wind and engine noise, but still allow you to hear human speech and other environment sounds.

Moulded ones invariably start leaking after 2-3 years, because the shape of the human ear canal changes over the years.

If you do go for moulded get soft ones. They are more comfortable, and the hard ones can transfer vibrations from the helmet right into your ear if they touch the helmet.

I used the moulded ones for a couple of years, but went back to the foam ones.

Alpine also make a nice compromise: http://alpineearplugs.com/prod_motosafe.htm Include filters, significantly cheaper than the moulded plugs, but still expensive compared to foam.