Unless the wizard has had some major upgrade in Nu52 of Merlin got nurfed, Merlin with ease.
The wizard has many consistent losses to his son and Daughter in solo fights. The only good showing of both was in reign in hell where after prepping and attacking a weakened hell they could face and defeat the triumverate (with the two of them together). Merlin by contrast has defeated Azezal (one of the orignial triumverate) and defeated Etrigan after he defeated the new triumverate (Etrigan and Merlin's father Belial had replaced Azezal)
The vast majority of the Wizards power is tied up containing the seven deadly sins. It's why he had to release them to someone else to be able to fight Spectre in DoV and why he had to get Ibis to contain them on the one and only accasion he defeated his daughter Lady Blaze.