I vote for guild coins - and no option to buy event resources for guild coins. ( some already has many guild coins in store )
event resources would not be fair to those not in guilds and if quest rewards are as now then high lvl players and players in large guilds would get more event items than other.
solution could be, if it with new guild quest system is possible, that during events all ( in guild or not ) get same series of quest ( maybe staged acording to level ) and same reward.
but that would just be as normal event quests.