Of course demand!
Even there are scarce or huge amount of supply if the demand is low, price won't keep hike. If I am looking for a coin, I usually look upon the volume of it and if the price is congruent to the total supply. Most of the time, I am buying coins which has lower supply because it will have the tendency to rise up when the demand gets higher. Lower supply will easily up while higher supply won't.
Yes.I also think it will be good to focus more on demand rather than its supply.If majority of the people and even big establishments will come to patronize bitcoin not just as an investment but as a currency,i'm sure the market price will continue to grow even more and even reach new heights in the future.