4.5 billion isnt hard to accept, if it were true, but the plain normal reading of genesis and the evidence supports six days better.
What evidence is there to support the theory that what appears to be 4.5 billion years worth of uranium decay happened in less than 6000 years, without releasing the amount of heat that should have been associated with that decay?
Actually, neither support the concept of a young earth. Here's a short word study I did on the yom, the main word that YECs rely on for their Biblical interpretation. It also links to refutations of some of the "scientific" claims for a young earth.
The simple fact is that all of the scientific evidence points to an old universe and old earth, and this evidence agrees perfectly with the Bible.