What kind of plot ideas do you have? The Realms is big enough that you can find just about anything in different places. If you want to do a heavily political game, you're going to use a different spot than if you want to do wilderness fighting and some dungeons.
Personally, I usually use either the Moonsea region or the area around Waterdeep for my campaigns, for the simple reason that those are the areas I know the best. Not that I've done a Realms game in a couple of years, mind.