The top title is the one that's on Raw, whether it's the WHC or the WWE title.
I keep on hearing a lot of ppl asserting this, but this is not always true. The entirety of 2005 focused on the WHC which resides in Smackdown under Batista where it main-evented or went high in the card over WWE Title in Royal Rumble, Wrestlemania, Vengeance, and Summerslam.
Here's what I think which title was more dominant for every year in the past:
2002: WHC (Raw)- carried by Triple H
2003: WHC (Raw)- HHH
2004: WHC (Raw)- HHH
2005: WHC (Smackdown)- Batista
2006: Even; WHC (SD)- Batista; WWE (Raw)- Cena
2007: WWE (Raw)- Cena
2008: WWE (Raw)- Orton, HHH and Edge
2009: Even; WWE (Raw)- Orton and Cena; WHC (Smackdown)- Hardy and Punk
2010: WWE (Raw)- Cena
2011: WWE (Raw)- Cena and Punk
2012: WWE (Raw)- Punk
2013: Hoping there would be an equal share of spotlight once again.
I really think the brand-union hurt the credibility of the WHC since its weekly presence made it look inferior to the WWE Title. A world title should always be the crown jewel of the show.