What are the top places in Bulgaria to get the best currency exchange rates, and how do banks, licensed exchange bureaus, and popular city-center providers compare in terms of rates, fees, and reliability? Additionally, how do different locations such as airports, tourist areas, and local markets impact the exchange rates offered to customers? Furthermore, what key factors such as exchange margins, hidden charges, and real-time currency rates should be considered to ensure the most favorable currency exchange experience in Bulgaria?