The New York is a pretty good burger imo when that is out.
Of others mentioned above, had a Patty & Bun, Honest Burger and Bleecker Recently.
Of those would go Patty and Bun top, Honest 2nd, Bleecker 3rd.
Patty and Bun was very good, had the Ari Gold with Fries with chicken skin mayo...very nice. Cooked perfectly, a good size portion.
Honest was also very good, just didnt feel like it was as special as others say, but each to our own!
Bleecker was a disappointment for me. Small burger, the bun was really not great compared to the others, just seemed like a seseme bun like you would pick up in a supermarket. Fries were small also considering the price.
Have had Leon's offerings also, wouldnt go burger there in future but their Chicken Satay box and Thai Green Curry box are excellent. Their menu for kids is great value too, better then a happy meal! I know i'm steering away from burgers, but for quick service places in London current favourites are Coco di Mama, and Yolk in New Street Square. Well worth a visit