I have flown TK and Easyjet extensively on this route. Both are fine. The TK food is quite good and the lounge at IST is a real spectacle and has great food. However, for political reasons due to president Erdogan's behavior, I won't fly TK anymore. I think Easyjet is just fine and fly this route a few times a year. I find LGW to be better than LTN for a lot of reasons on Easyjet. Unless TK is much much cheaper, I'd suggest Easyjet.