I just want to make sure we're on the same page here.
It seems to me like you a talking about enemy attack vs. player defense (and enemy damage vs. player hp).
I think monsters, NPCs and PCs should be based on the same math. Hence, I meant both ways, assuming PC fighter against NPC fighter. Other classes can have somewhat different to-hit chances.
That doesn't mean you need to create NPCs as PCs (but you can). It also doesn't mean there can't be a lot of monsters that have lower AC and higher hp (against which PC hit chances are better). The main wish I have is that to-hit chances improve instead of the "running in place" feeling of 4e (and to a degree 3e).