Most often, receptions start off with a toast by the best man -- but preceding this gesture, a welcome speech from the host is a nice touch. Pair it with a blessing, and it can come right before the food!
But who's the host? Technically it's whoever's name is on the host line of the invitation, which is, traditionally, the father of the bride. However, in many situations, the true hosts (no matter what the paperwork says) are the bridal couple. (When my colleague Lauren Richel Kelly married, her dad insisted that the couple officially welcome people -- he wanted them to shine instead of him.)
Whichever way you decide, making an official speech to welcome guests isn't a substitute for your personal, face-to-face greeting. It is, however, a really nice moment to commence the festivities.
Will you have a welcome speech at your wedding? Who would give it, in your family?