When I took a cooking class from a local Mexican chef (here in DC she's the chef at the Mexican Cultural Institute), she highly suggested we use Ceylon cinnamon sticks where cinnamon was called for in her recipes. In particular, I used it when I make her mole sauce. I see that Penzey's mentions use of the Ceylon cinnamon in Mexico. If you're making Mexican food, I'd go with Ceylon!

Penzey's sells four types of cinnamon. Here are their descriptions for each one:

Ceylon Cinnamon --
Complex and fragrant, with a citrus overtone and rich buff color. Although Ceylon cinnamon is less strong, its hint of citrusy flavor and lack of any bite whatsoever makes it the favorite in both England and Mexico where it is preferred for all uses. Ceylon 00000 Cinnamon, ground, from Sri Lanka.

China Tung Hing Cinnamon --
Extra sweet, spicy and strong. Perfect for everything from cinnamon rolls to apple pie, Christmas cookies to French toast. China cinnamon is perfect for cinnamon sugar—mix 2-3 tsp. in 1/ 2 cup granulated sugar and keep it on the table. Sprinkle in pancake and waffle batter, shake on oatmeal and cream of wheat, yogurt and fresh fruit.

Korintje Indonesia Cinnamon --
Sweet and mellow, Korintje cinnamon is the type of cinnamon we all remember from our childhood. Fragrant Korintje cinnamon is as strong as China cinnamon, but smoother and not as nippy. We love Korintje cinnamon for sprinkling—on hot cereal, oatmeal and cream of wheat, French toast, pancakes and waffles, sugar cookies, and pie crusts. Perfect for cinnamon breads, quick, yeast, or toasted with raisins.

Vietnamese Extra Fancy Cinnamon --
Vietnamese cinnamon is the strongest, richest, and sweetest cinnamon around. For traditional cinnamon recipes such as gooey cinnamon rolls, the vibrant flavor of Vietnamese cinnamon really shines. It is so strong, that in most recipes it should be cut back by about a third, but it is perfect used full strength in any recipe where cinnamon is the main, delicious flavor. Ground, from Vietnam.

Anything labelled Vietnamese or Saigon cinnamon is generally cassia and is definitely my go-to for a lovely traditional cinnamon flavor in both sweet and savoury applications. Ceylon cinnamon is also nice but has more of that "red-hot candy" type of cinnamon flavor, less woodsy than cassia. Hope this helps!

I will also go with cassia for this. It's sold in a flake form rather than sticks. But you still have to grind it up---preferrably with a mortar and pestel.

AJ, I've struggled with this also. I always thought I hated cinnamon (except for apple pie and cinnamon flavored chewing gum--go figure). I finally discovered a cinnamon that I love and use exclusively--Penzey's extra fancy Vietnamese Cassia Cinnamon. I found it through Cook's Illustrated--they had an extensive review of cinnamons with an explanation of what accounts for complexity of flavor. I'm not sure if you have to be a member to read the review. Here's the link: http://www.cooksillustrated.com/tastetests/overview.asp?docid=20990

If you can't open it, let me know and I'll copy and paste it into an email and send it to you.