For a wedding, foil balloons are a great choice. Their ability to hold helium and therefore float for much longer than the latex equivalent, gives them some brilliant advantages. First, if you are preparing them yourself, or a relative of friend is getting the venue ready for you, the longevity of a foil balloon is a big bonus, as they can be inflated and left in place the day before the wedding, and you need have no concerns about any of them looking limp on the day. Although it's very rare, even if one has gone a little limp, you can just give it a quick additional puff of helium and it will be absolutely perfect again for the reception. In addition, they just don't burst - or at least, not without a significant level of force, so accidental damage to one of these balloons is extremely unlikely.
Foils are larger than other balloons and so you need less of them. We would normally recommend that just two balloons were used in a table display, as the greater size means that anything more than this creates a feeling of overkill. Two contrasting colours that fit the theme that you have chosen for your day works extremely well, and of course if you choose a message balloon (printed with a good luck slogan) this can be set off by another of an alternative colour.
Set the two balloons apart in height by about two thirds of the diameter of one, and then make sure that the lowest of the two sits at about two feet above the surface of the table at least - this ensures that your guests aren't ducking underneath your decorations in order to be able to talk to one another. Match the ribbon colour with the balloons and tie them to a weight of your choice in the centre of the table.