Sticks made from softwood are lighter coloured than the darker hardwood, and they tend to "break-in" easier.
Hardwood sticks are a little heavier, and have a more solid 'feel' when playing your bowl.
A wood/leather stick offers two different ways to sound your bowl.
Tapping or playing the bowl with the leather part of the stick brings out more of the lower frequencies, particularly in the old "master" bowls. The large stick, because of it's large diameter of leather, is used primarily with the leather end on larger bowls
Tapping or playing your bowl with the wooden part of the stick brings out the higher frequencies.