The 320D is always going to be the more sensible and better all-round car. It'll average a good 10mpg more than the 330D driven the same, is cheaper to tax and run and whatnot and will be a little more nimble in the bends due to lower weight.
The 330D is just the "better" car, but not when taken against cost. it's the luxury version. none of us bought a 330D thinking it was the "sensible choice"
We bought them because we wanted a 250bhp diesel that'll return 40mpg and because we can