My friends and I stayed at the Payidar Hotel during our visit to Istanbul. I'd say it's on the quietest central street in Mecidiyeköy. The hotel is beautiful; I especially liked the rooms with balconies open on all four sides. The staff were very friendly and attentive; we felt right at home. They offered complimentary tea, coffee, and water for four days. The location is very central, they have a small parking lot, but since it's in a respectable area, we didn't have any parking problems. I highly recommend this hotel, which is very clean and quiet, and ideal for those who want to truly relax.