Most SIN-IST flights feature the Airbus A330-300s with full flat seats, which I prefer over Boeing 777-300ERs. 2-2-2 is better than 2-3-2.
The seats are okay, and the entertainment system is surprisingly very good as well. The food in general is excellent despite there is a lack of variety for frequent flyers. If you like Mediterranean food, you will like TK food. I love their beef dishes and the appetizer trolley.
The major issue with TK is the crews - they are really not trained properly and lack the polish. They are a bit distant and you have to use your call buttons frequently.
I will say if you get a good fare, go with it. But if SQ is priced the same, I will go with SQ.
Carfield