The D28 and D35 are both rosewood back and sides instruments by Martin. The primary difference is that the D28 is a 2-pc back and the D35 is a 3-pc back with some more ornamentation.

Both models originally used Brazilian rosewood, but I believe as that material became harder to come by in the early 1970s time frame, Indian rosewood was used in regular production.

The only guitar in the Martin Standard Series of dreadnoughts made with a mahogony back and sides is the D18.

I feel that the mahogany instruments tend to be somewhat brighter and crisper in the high and mid range while not quite as full in the bass response.