ok...this is no trick question
well..poly is better if you want to do it quick n fast. polygon modeling is very fast for organic characters..as you just cut and move....therefore a more robust toolkit.
NURBS, was the better option before..for organic modelling due to its infinite smoothness
, but now the general trend for its usage is more in the CAD CAM industry where it is used widely.
NURBS gives a real smooth and ordered surface, also premade UVs..so..if ya wanna make pipes n other basic primitive based models..this is the way to go!
But if you wanna make organic characters...you will have to contend with..lathes, fillets...and so on..modeling in NURBs is much more technical than poly
The plugins T-Splines in Maya and Power NURBS in 3dsmax provide a decent NURBS based alternatives to polymodeling.