Just use poly's and you'll be fine
You have a point with the level of detail you can control easily, but the only time i even considered using nurbs was when i was working on a psp game (a programmer told me that the ps series supported nurbs very well) but in the end we decided to go for poly's anyways.
Some wips of a Jagdpanther tank im working on (with baked lightmaps). It's on 8600 poly's and i want to use as a prop in a DoD map. Don't have a clue what the map is gonna look like, but i just felt like making a jagdpanther
And some older wips: