Borg, easily. As others have said
(1) the Daleks can't even climb stairs
(2) they repeatedly lose to ONE GUY who's usually unarmed except for a sonic screwdriver. Verrry intimidating.
(3) the Borg "collective voice" is much scarier than the Dalek's hysterical and high-pitched whines.
(4) the Daleks don't have any ability to match the Borg's adaptation ability