Istanbul has over 300 mosques. During my Istanbul Art Trip, I managed to visit five in the city. I was only in that part of town for a week before I ventured to the Asian side and saw the beautiful mosques of Uskudar.
5- (Sultan Ahmet) Blue Mosque
This is one of the most obvious mosque options because it's right there in the centre. Prepare yourself to see masses of people
4- Aya Sophia
The same crowdedness applies to this one too. It is really interesting to see the old Christian art along side the Islamic one. I felt that is what diversity is all about.
2- Rustum Pasa Camii
The tiles were interesting in this one. It's actually known for its Iznik tiles. There is a book stand in the courtyard that sells books about the tiles found in there. We had to walk through a very busy market to get to it. It was distracting to look at the market stalls, but we got there. We did a little drawing session there as well, which was really nice.
1- Sulymania Camii -top pick-
Very grand and stunning inside and outside. I liked the view of Istanbul from there. If you don't have time to go to all five, I would recommend this one over the rest.