I think I'll go with the Danes on here regarding Viktor Fischer being the player with most potential. Thing is, I doubt Fischer is ready for the EPL from next season already, but if Spurs don't act soon he'll soon be priced out of Spurs' range.
Eriksen, as our Danish "scouts" have pointed out, is a rather erratic player - one moment he's top class, the next mediocre. Something Eriksen himself commented on a few months ago, when he said he need to work on his motivation when playing against "lesser" teams.
Exactly... The player that would be most useful currently would be Eriksen, as he's the most developed of the three. The player with the biggest potential is probably Fischer, while Cornelius would get games due to our current striker situation, but would be far from an established player if we signed him now.