I would choose the axela. Performance, handling, safety, options and looks are all better than any other jap car in that price range. Spare parts are plenty and the costs are reasonable. Demio is a hatch and the axela/3 are sedans with more space, options, power and better looks. Search the forum, you will be able to find more info about these cars and what to look for before you buy one.
Also read this for more info about the axela.