I would say that you would usually use scent for a nice smell and odour for a nasty smell. For example, you would talk about the sweet, heady scent of her perfume but the rancid, cheesy odour of his feet.
"Scent" can be a verb as well as a noun. There are also conventional uses of one word or the other - "the odour of sanctity", hounds following a scent or scenting their quarry, and the metaphorical use of "being in bad odour".
well yes but you might talk about "the odour of pine trees" Indie I reckon part of the difference, as well as the noun/ verb thing, in "literature" at least, is whether a one or two syllable word fits the rhythm of the writing.