A good one. The general rule of thumb is to cook with a wine you would be happy drinking, because your finished dish is only going to be as good as the ingredients that go into it.
Madeleine Kamman, author of the exceptional but daunting The New Making of a Cook (Canada, UK) offers the following advice:
"If a recipe calls for dry white wine without mentioning the type of wine, use any good dry white wine such as Sauvignon Blanc, if you are a complete beginner, or a Chardonnay if you are a little more experienced and know how to cope with the relatively larger degree of acidity surfacing when Chardonnay wine is reduced. If Sauvignon and Chardonnay are too expensive, use generic wine that tastes round in the mouth just after opening the bottle."