Each species of wood will create a slightly different sound. On an ukulele the wood difference is not as pronounced as it is in guitars because the wood surfaces are smaller. I will list qualities either from my own experience or as described by other sources.
New instruments will tend to sound better with time as they are played more. Old instruments will almost always sound better because the resins have hardened in line with vibrations created by the instrument. The resins in the wood of new instruments will shift and align with the vibrations over time and improve with age.
BACK AND SIDE WOODS:
Koa – From Hawaii is a member of acacia family and has a mellow tone. It is an open pore wood and is becoming more rare. Therefore there may be more defects in the wood than there used to be. The rarity is also reflected in the price. Koa can also be used as a top for an all Koa ukulele.
Honduran Mahogany – Ukuleles made from this will have a “strong midrange, excellent punch, and good sustain.” Lmii.com
“warm familiar ukulele tone” stewmac.com.
It also has an open pores and a sound close to Koa, and therefore one of the most common ukulele woods. The color starts out golden, but turns darker with age.
Claro Walnut– Also called California Walnut because it is a cross between the English Walnut and the native California Black Walnut.
“Claro walnut is often described tonally as Rosewood,,,,on steroids. The sound is full and rich and clear with great resonance. The colors can vary wildly, but always range from elegant to outrageous” Ukuleletonewood.com
Black Walnut– “Many describe Black Walnut’s tone as falling naturally between rosewood and mahogany. Walnut’s low-end response is strong and closer to that of a rosewood, while its mids and highs tend to be more organic and warm.” Stewmac.com
Amazon Rosewood– available occasionally. “The sound of Amazon Rosewood is very similar to Brazilian Rosewood and some would say better!” LMII.com
Indian Rosewood– A guitar standard. “The vast majority of the higher quality steel string and classical guitars made over the last thirty years have been made from Indian Rosewood. Many of the top classical guitar makers preferred it to Brazilian Rosewood for many reasons. It is a beautiful wood…and the sound produced by Indian Rosewood guitars is superlative.” LMII.com
Southeast Asian Rosewood– “Few woods compare with Brazilian Rosewood as nicely as this one and it’s superb density has led many to claim that it is superior. Our sets exhibit an extremely lively, sonorous tap tone. The color ranges from a warm brick-red to an attractive rust-brown color. Less porous than most Rosewoods, it finishes nicely” LMII.com
Cocobolo Rosewood– “Cocobolo Rosewood grows in southern Mexico and Central America. It’s a beautiful wood, which when freshly cut shows bright yellow and orange-red colors. Over time it mellows to a rich brown-red color with black streaks. It is probably as close to Brazilian Rosewood in beauty and tonal qualities as any wood.” LMII.com
Sitka Spruce– “Known for its bright top end and clear lows, Sitka Spruce also has fantastic volume projection.” Stewmac.com
It is a very stiff wood considering how soft it is. Makes for a brighter sounding ukulele.
Port Orford Cedar– “A rare, hard variety of Cypress, very light in weight with incredible strength. It fashions and fabricates with no issues and finishes with a glass like smoothness. POC is also amazingly resonant with tonal qualities second to none. The sound is similar to Redwood, a bit less bright with full rich sound.”
I find it makes for a wonderful rich sound and has a beautiful fragrance that emanates from the soundhole as it is being played.
Western Red Cedar– It has a much warmer tone than spruce. It is also a softer wood than spruce and the surface will tend to mar or dent more easily. However it does create a warm island sound.
Redwood- “Considered by many to be the King of tonewood, Redwood is incredibly resonant with awesome harmonic development, projection and sustain. Redwood ukuleles have a truly magnificent sound.” Ukuletonewood.com
“The dark color tones of a Redwood top are not at all traditional, but the superior musical tone of these soundboards win out over their unconventional appearance. Some are clear color and some have the idiosyncratic streaks and coloration of this species.” LMII.com
Douglas Fir- “It was a real surprise to find that Douglas fir was actually four times as resonant as Sitka Spruce. The sound is warm, yet crisp and clear at the same time with excellent harmonic development… and will yield fantastic sounding ukuleles.” Ukuleletonewood.com