There may seem to be little to choose between the two, but let's not forget that Lewis's right hand did the business at a higher level than what Wlad has yet to see. Levels aside, I would still choose Lewis, I think he threw his right hand with a bit more natural ability.
Lewis was definitely more inclined to open up with his right, committed more to the punch, being guilty of winging at times. Wlad has a more balanced offensive arsenal, and has been more paced since his disastors, so we see less of the right.
I think Lennox's one-punch power in his right hand is greater than that of Wlad's, although this might be because Wlad doesn't 'sit-down' on his punches as much as Lennox sometimes would. The punch Wlad hit Calvin Brock with, however, was about as devastating a right hand as any you will ever see. Still, IMO, edge to Lewis.