Are these narratives different because one was written by Judeans and the other by Israelis? The conflict in question was, after all, a "Civil" War.
It seems funny that this is backwards. The Israelis say that they didn't win and then had their capital taken and their king killed by the Assyrians. The Judeans say the Israelis did win and the Assyrians didn't help.
I vote that the Kings account is accurate, and that's why the Israeli's gave the negative version about themselves. It's what happened. The Judean version is inaccurate, and the historian wrote it that way because Ahaz "didn't do what was right in the sight of the LORD," and so he didn't want Ahaz to look blessed.
Pure speculation, of course, and likely worthless, but fun.
This is Truthlover, by the way. I accidentally banished myself from the boards by changing my email address but making a mistake. My new password was mailed into limbo. I'm waiting to see if Percy is going to rescue me.