The Piemonte area, or Umbria, eastern Tuscany, Le Marche, and the upland parts of Emilia Romagna are the best places. To enjoy the prized white truffles, you'd have to be there when they're in season, which is from mid October to late November, more or less. This year, there were virtually no truffles to be found, for various climactic reasons, so next October would be your next chance.
The best black truffles are the winter truffles, which are found up until about March. The least expensive are the summer truffles, also called scorzoni.
If you want the best truffles, you have to go to a really trustworthy restaurant. Some restaurants serve imported truffles of low quality, which suffer further deterioration during the trip.