Bathroom
Steam, tile, and a candle that doesn't compete.
The room
The bathroom wants a scent that doesn't fight the steam. Fresh, green, or citrus — nothing that turns cloying when it gets wet.
What to burn
scent fig, or bergamot level one candle, on the sink when before a bath or shower avoid heavy amber
The point
Steam is a diffuser you already have. A small candle in a hot bathroom does the work of a bigger one anywhere else.