TK has the best business class by far inside Europe and also one of the best in terms of long haul flights. I just recently flied to YUL with old style B777 with 2 +3+2 config and even though it lacked the better experience of cabin style A350s, service and quality was amazing. I just switched my seat to corridor instead of window to not annoy the guy sitting next to me...
Istanbul Airport of course has a business lounge and although it is very crowded, food and faculties are quite satisfactory and not much lines for food or drinks. However IMHO new airport sucks.

PS: If you get lucky, you may fly with the new A350s, but I don't know which routes they fly.