I've eaten chicken tikka all over the world (yes, including famous establishments in Mumbai and Delhi too). Of all of the different kinds I have tried, Bombay Palace in LONDON (not in New York or any other branch) is the clear winner. Marinated and cooked to absolute perfection, these delicious morsels of chicken take the cake. Even when I have gotten take out from Bombay Palace, the chicken is still incredibly tender even after it's been carted around by me for 20 minutes en route to where I am staying.
Enjoy this chicken with some red onions and lemon, and some naan. It's not cheap, but it's definitely worth the splurge.
Bombay Palace is located in central London on Connaught Street.