What is responsible for black tarnish on silver? Silver on being exposed to air, forms a black film. Now my question is whether the film is silver sulphide (due to reaction with hydrogen sulphide in air) or silver oxide.

Both compounds are black.

In my view it would be silver oxide because oxygen is more abundant and, intuitively, silver seems react to oxygen faster than hydrogen sulphide- oxygen is more reactive than hydrogen sulphide. 

But a little google search loosely hints it is silver sulphide. Any suggestions on this too?
There is no such thing as "being reactive". Say, you have A and B; some compounds tend to react with A and not with B, and some would react with B and not with A. Which is more reactive? You can't tell; you can't even ask this question, for it's meaningless.

Black tarnish on silver is mostly silver sulphide, as confirmed experimentally. I'd even say that silver does not form a black film on being exposed to air, unless there is some source of hydrogen sulphide nearby (raw eggs, sewage pools, or something else).

It is just that $\ce{Ag}$ tends to prefer $\ce{S}$ over $\ce{O}$. Many other heavier metals are like that, and many lighter metals have different preferences. This is explained (kind of) by the hard/soft acids/bases concept.

So it goes.