Now that I recently upgraded my acoustic guitar, the top soundboard wood is Sitka Spruce and the back and side woods are Cocobolo (Mexican Rosewood). Apologies as the contents of this post will be very guitar geekish.
When buying an acoustic guitar, it’s all about your preferred tone and how you primarily plan on playing it (mostly strumming, flatpicking, or fingerstyle). Tone is derived from the woods the guitar is made out of. 80% of the tone comes from the wood on the soundboard (top of the guitar), while the other 20% comes from the wood on the back and sides of the guitar. Mixing and matching different tops to different back and sides allows for a variety of tone to pick from when trying to find that preferred tone.
In general, Sitka Spruce (sometimes Bearclaw Sitka Spruce) is used as the soundboard for most guitars manufactured today. It is one of the most dense woods out there, making the volume ceiling high. Sitka is best used for strumming and aggressive flatpicking where you can really drive the volume up when playing. On guitars manufactured prior to WWII (pre-war), Adirondack Spruce was used commonly for soundboards. Adirondack is even more dense than Sitka meaning you can drive the volume even higher. Guitars made with Adirondack generally sound like cannons.
In contrast, Western Red Cedar for the guitar soundboard is best for fingerstyle players (sometimes flatpickers). Most classical guitars have soundboards made with cedar. Cedar creates a “warmer sound”, but has a low volume ceiling. Strummers and aggressive flatpickers will reach the volume ceiling fairly quickly and get frustrated.
Some other woods such as Redwood, Koa, Mahogany may be used for top wood as well. Each offers a unique sound of its own to be experienced.
From the Breedlove Guitars website, here is their chart for tones on top woods and back/side woods:
Back and Side Woods
In general, Maple is the brightest sounding wood. Maple can “cut through” when playing in a band setting. The rosewoods (Indian Rosewood, Cocobolo, Madagascar Rosewood, and the hard-to-find/get Brazilian Rosewood), on the other hand, are the darker sounding woods which accentuate more bass.
From the Taylor Guitars website, here is their chart on tonewoods (dotted-line means the wood has the potential to reach the frequency as it is played more over time):
For strummers, an Adirondack/Rosewood guitar would work best. However, since these guitars are generally more expensive and harder to find, a Sitka/Rosewood guitar is recommended.
For fingerstyle players, Cedar/Koa or Cedar/Mahogany are tried combinations that work well.
The size of the guitar body may also determine the guitar tone as well. Naturally, a smaller body grand concert or OO guitar will yield less volume and often bring out more of the trebles over a larger body dreadnought or jumbo guitar. Think about comparing a violin to a double bass.
Martin Guitars put out the following subjective tone chart in one of their members’ magazines:
The Taylor Guitar Forum (now the Acoustic Guitar Forum) and the Unofficial Martin Guitar Forum are the two biggest guitar forums out there, which corresponds to their respective guitar manufacturer. Other guitar manufacturers have forums out there to discuss any guitar issues as well.