Cellulose vs. Fibreglass.
Cellulose is the insulation of choice. Fibreglass is good, too, but it has a lower insulative value.
Cellulose is made from recycled materials, is fire resistant class-1 fire rating thanks to its treatment houses that catch fire burn slower with cellulose installed than with fiberglass.
Cellulose provides better sound insulation than fiberglass - homes are less noisy with cellulose.
Fibreglass is a suspected carcinogen and carries a hazard warning label. Cellulose is much near benign.
Many fiberglass installers "fluff" the fiber with extra air, so you don't get as much insulation as you're supposed to. This trickery can't easily be done with cellulose, and certainly not to the extent that as with fibreglass.
Fibreglass settles much more than cellulose, like a box of cereal. So over time you actually get fewer inches of fiberglass than you paid for resulting in more heat loss to your attic.
Ventilation might seem like a minor consideration, but when done properly, it can extend the life of your attic, insulation, roof structure and shingles saving you hundreds of dollars in repair costs.
In the summer, hot, moist air in the attic can effect roof sheathing and cause shingles to deteriorate. A hot attic also makes a home more difficult to cool, results to over worked air cooling and in added energy costs.
In the winter, heat loss in an attic melts snow and can form ice dams at the roof edge. Water can back up under your shingles, wetting, damaging, insulation and eventually the structure of the roof itself. Ice dams can even cause leaks inside your home, resulting in drywall damage. Mould also flourishes in humid attics.
Drafts & Air Leakage
Ensure exhaust venting is insulated, pot lights are protected, electrical wires & fixtures are sealed to prevent drafts and heat loss to attic. It will also help prevent the establishing of mould growth caused by moisture.
Attic insulation with proper ventilation and sealing drafts etc. provides you more comfort and will save 30-40% in energy bills.