In the PHB, it says:
"A paladin using a holy sword projects a circle of power 30' in diameter when the sword is unsheathed and held. This power dispels hostile magic at a level up to the paladin's experience level."
But in the DMG, it says:
"In the hands of a paladin, however, it creates a magic resistance of 50% in a 5' radius, dispels magic in a 5' radius at the level of magic use equal to the experience level of the paladin..."
Well, a 5' radius does not equal a 30' diameter unless you're using Cthulian geometry!

A 30' diameter seems a bit huge to me, and I always thought the DMG trumped the PHB as far as details on weapons and what not go. So I believe we always used the 5' radius thing, which is still a pretty good sized area. It's basically a 10' diameter circle.
How have the rest of you handled this?