Britney's songs are often very well constructed and composed, but poorly executed and overproduced. Baby One More Time is especcialy good, I once heard a cover by someone with just vocals and guitar, and it astounded me how good the actual song is.
I'm not saying I like her, but most people are bashing her cause she is about the most commercial and marketed person in music today.
I can't comment on the Versus cause I haven't heard enough No Doubt to build a solid opinion on. But I'd the comparison isn't as uneven as some people make it seem.