Using superlative is always relative to the persons point of view. There are too many factors- price, taste, ease of reaching the place, presentation, service which can be arranged in number of ways to get your best place. May be not the "best" indian curry in Zurich, but I can recommend these to try out. They are NOT "real" restaurants

but yeah would do the same job.
For people in and around Central Tram Stop Zurich:
India Gate Oriental Store
Beckenhofstrasse 16 8006 Zürich
Price-> 8-12CHF
Bombay Karachi Take-Away
Stampfenbachstrasse 32 8006 Zürich
Price Range->13-18CHF
To be honest, I have been only to one or two restaurants in Zurich which seemed to me little overpriced. But I agree, that may be because I find much better "curry" at my own home cooked by my wife or myself!
I can't be sure, but I think the people who have commented here DO like to have India food like the way it should be (which means spicy and not westernised indian food

). Also I am sure you knowledgeable folks also had the same trouble explaining every interested spook around you that you really cannot being 'curry powder' from india when you come back from a holiday!

Because there IS NO such thing ...
Reading all this, I think we might once try this Khans ... sounds tasty! ~smack~
Though Banana leaves and Naan is an odd combination ...