Indeed, it depends:
Some dry white ports can be drunk at cellar temperature (e.g. Churchill), but I still like them better slightly chilled. All of the medium sweet or full sweet (lagrima) types are best when chilled.
Most white ports are fairly undrinkable on their own and show best when mixed with tonic, ice and lime.
Exceptions: Niepoort dry white, Churchill, Quinta da Casa Amarela, Quinta de Baldias, which are all very good.