There is an interesting piece in Cook's Illustrated which analyses the taste of ready-ground cinnamon from a variety of sources - in this case, cinnamon cassia which American tastes prefer.
They assess cinnamon according to heat, complexity of flavour, and texture. If you're interested it's worth ploughing through the whole article, but the short of it is that:
1 Volatile oils give cinnamon its distinctive flavour; the more, the better.
2 Much of these volatile oils can be lost during the industrial grinding process "under the heat generated by whirring blades."
3 To avoid this, some companies use a cold process called cryogenic grinding (ughh!!)
4 The most important factor was freshness. (While we don't disagree with this conclusion, there didn't seem to be any way of measuring the freshness - perhaps they went by the sell-by date, which is often measured in years).
Anyway the winner was Extra Fancy Vietnamese Cassia Cinnamon: "Slightly smoky" and filled with complex "warm clove" and "fruity" flavours, its spiciness was "strong, yet not overpowering"; it "started mellow, then built to a spicy finish". It had the most volatile oil content of all the samples.
We can't help pointing out that our graters do not affect the volatile oils at all. Further, our Saigon cinnamon is fresher than any other cinnamon available - see the harvest date - and has very high volatile oils. One way to prove it is to light it: it catches fire and sizzles. Only really fresh, really good cinnamon cassia will do this. Take a look.