Tyres have a designated size (700x28) but there can be a wide variation in the actual physical width of the tyre.
For most hybrid style rims, 28mm is the narrowest that you should use, and it is a good size for fast general purpose riding.
What type of riding do you do (fitness, commuting/utility, training, all weather?). How rough are the roads.

I use 28mm on my all-round road bike/commuter/utility machine, but avoid the narrower types of this designation which are really 25mm in size.