Cedar VS Spruce
Unfortunately, there is no definitive answer here, however, there is some consensus.
Spruce is the most popular tone wood for soundboards. Probably because its tonal qualities work well overall. Spruce is said to have a sweet, smooth, slightly bright tone, yet warm enough that it doesn’t sound thin. Spruce sounds good when combined with just about any other tonewood. In addition, it also has pretty good projection and volume. Spruce is said to improve over time.
Spruce is a common species of wood making it reasonably sustainable. Sitka spruce is the most commonly found type, with grain varieties such as ‘bear claw’ adding to the aesthetic appeal. Sitka is characterized by its clear fundamental harmonics. Other varieties used are Adirondack, Englemann and Lutz.
Engleman spruce is typically from North America, and has a warmer, creamier tone than Sitka. Adirondack is a lesser-used type of Spruce, with a louder and brasher tone. Lutz Spruce is a naturally occurring hybrid, growing among the Sitka and White Spruce in Western North America. It picks up a bit of each wood's character: high stiffness, low density, and consistent white color.
Cedar is probably the second most popular material for soundboards.
When compared to spruce, cedar is lot less dense. This makes it quieter, less bright, with less sustain, however, Cedar is much warmer with wonderful overtones and takes less time to reach its full tonal potential.
As a result, Cedar is a popular choice with classical and fingerstyle players.
Western red cedar has only been in use as a tonewood for about 50 years.
Grown in the Pacific Northwest, it has come under a lot of pressure from logging and many of the old growth forests are restricted from further harvesting.
I personally think there is way to much debate over this subject and that if guitarist are insistent on obsessing over something then it ought to be on improving there playing skills not the subtle differences between tonewoods.
I recommend sampling a few cedar and spruce tops in the same price point so that you can make an informed decision.