Red or white?
Top glass-makers sell up to 15 differently shaped glasses for every variety of wine. While that might be a bit more than you need, there are differences between reds and whites that can be exploited by choosing the right glass. Reds, with their rich tannins and deep aromas, benefit from more exposure to air, so large globes make sense. Whites need to breathe less, and often are fruitier to begin with, so a smaller glass works well, plus it helps to keep the wine cool longer. If you feel like presenting your wine with flair, consider having a set for red and a set for white.

Stems or stemless?
Wine glasses generally sit on a stem so that you don't warm the wine with your hand when you pick it up, and so that your fingers (and fingerprints) don't get in the way of looking at the wine. That said, in Europe, wine is often served at dinner in simple glass tumblers, and the tumbler has started to take hold here in America, too. It's an unpretentious and casual way to go, they're easier to wash, and harder to knock over. They're better for red than for white wines, since the heat from your fingers will gradually warm the white wines.

Be clear.
Whatever shape or size you choose, be sure your glass is clear. Tinted or opaque glasses will prevent you from seeing both the true color of the wine and how it behaves in the glass when swirled.

The one and only.
If you must only choose one glass, choose a glass with a large bowl that tapers at the top (in the wine world, these are called "tulip-shaped"). The wide bowl will allow enough room for the wine to breath, and the narrow opening will focus the aromas for your enjoyment. This is the kind that is often used at wine tastings.

Wash by hand.
All the experts recommend washing your wine glasses in very hot water by hand and without soap to avoid building up a residue on the glass that can affect the flavor.