Is London's climate more like NYC or Istanbul?

Istanbul is very similar to London in winter, but summer isn't so clear cut.

Climates like Istanbul, Bordeaux, Bilbao, Samsun and Trabzon are essentially London turned up a bit and with some dry-summer and wet-winter tendencies.

New York City on the other hand is a classic East Coast climate of a greater landmass with strong seasonal differences. Due to Istanbul's lower seasonal range, the answer is rather obvious.

Definitely Istanbul. Although the rain pattern in London doesn’t vary so much apart from autumn which has more, in summer we are prone to drought and any rain falls in short showers generally. I couldn’t see NYC going three months without much rain like we did this year and have done on past occasions.

London is a colder, cloudier Istanbul. In your opening comment you seemed to be under the impression that this poll would be close 

Istanbul has slightly cooler summers, so closer to London. Drier than London, but NYC is wetter than London in the summer so London is about halfway. Istanbul isn't similar to London at all, but it's slightly closer to London than NYC

Is London's climate more like NYC or Göle?

I must say, I thought for sure it would be NYC - never looked at Istanbuls climatic averages; but its certainly closer to London than NYC is.

I used to point this out to a certain Spanish member when he kept boasted about 13 climate zones that were basically just altitude moderated versions of the same climate.