This is where looks and personal choice come into play.
The cost of materials is also greater for cedar shingles than for asphalt, as well as labor.
Asphalt are about 3' wide and it takes 4 nails to secure each shingle. Cedar shingles are any where from about 3" to 10" wide and each requires 2 nails to secure.
Asphalt are some what self alining, that is once you get the correct start you don't need to worry about the edge joints between shingles lining up. Cedar requires constant attention to the edge joints (because they are all random widths) to make sure that they don't line up.
In a mild climate cedar shingles will hold up very well. The fact that you have a steep roof will also be on the plus side.
Just remember if you live in a hot dry climate the life span of the cedar will suffer.
You may want to look at this web site. http://www.cedarbureau.org/