I use white wine because I generally prefer (and have on hand) white wine, but red wines work perfectly, as well.
I've never been much of a red wine drinker, but I really enjoy a lot of whites, and whenever I cook with wine I like to have a glass.
But, I've started using more red wines in my cooking, particularly Malbec for chili and Burgundy and Pinot Noir for stew, though, so adding whatever kind of wine you have on hand (or even hard spirits like gin or vodka) is perfectly OK.