It's hard to say over all, but certainly currently, I'll break it down like this.
WWE Championship. On March 28th, 1998, Steve Austin won his first WWE championship. This is at a time where I could say that the WWE Title was at it's most valuable. Why you might ask? The Current WWE roster at the time had Steve Austin, the current champion, and the Undertaker, a former 2 time champion. That's it. No one else on that roster held the WWE championship. Sure, guys like Simmons and Vader were on the roster, but that belt wasn't one they had acquired.
In the 35 years that title existed up to that date, the belt only changed hands 38 times. That's pretty damn impressive, nearly a title reign a year. Fast forward now, just a little more then eleven years later, and the WWE title has changed a total of 90 times!. That's 52 title changes in 11 years, for nearly 5 title reigns a year. That's ridiculous, and does nothign but belittle the legacy of that title, and everything that came before it.
Oh, but let's not stop there. Let's take a look at the WWE owned WCW Championship, which was converted into the World Heavyweight Championship. The WCW Championship was owned by the WWE for a little less then one year. Booker T was the incoming WCW champion, and lost the title to Kurt Angle in July. That title switched hands, from July to December, six times. A world title switched hands, on average, more then once a month. That title later merged into the Undisupted championship, and was resurrected intot eh World Championship in the fall of 2002.
In less then seven years, the World Championship has switched hands, not including those six, 29 times. That again, is around 4 champions per year. That is terrible.
If you combine both the WWE, and WHC since Wrestlemania 14, their has been 87 world championship reigns in one company. 87 championship reigns, in 11 years, and that's not including the ECW championship (which has a status in limbo of being a world title).
In my opinion, the most prestigous title in the world currently, does not exist in the WWE.