JKAsiege

My wife and I are planning a trip to Istanbul in September. We'd like to spend a few days in the city and then drive to some places outside Istanbul before flying home. I'm currently comparing different car rental options. Has anyone rented a vehicle there recently?

I'd suggest looking at Rent-Trip as one of the local options.
https://rent-trip.com/turkey/istanbul/
Their fleet includes everything from smaller economy cars to SUVs and more comfortable premium vehicles. For a couple with luggage, I'd probably choose something compact but comfortable enough for longer drives. They can also arrange delivery, which could be convenient if you don't want to visit a rental office after arriving. I'd send them your travel dates and ask what they have available at that time. Just make sure the final cost and rental conditions are clear before you book.