Is Gatwick Airport nearer that Stansted from the Tubes ?

Yes, no or maybe depending on where you want to go and how you want to get
there.

If we are talking about travelling by train to central London you can go
from Stansted to London Liverpool Street in about 45 minutes (Stansted
Express) though there are also slower trains. However the trains also call
at Tottenham Hale on the Victoria Line which is about 30 minutes from
Stansted and that line can take you into the heart of London too.

Likewise you can go from Gatwick to London Victoria in about 30 minutes
(Gatwick Express) but there are also slower and cheaper trains and also you
can go to London Bridge or King's Cross using the Thameslink trains in a
slightly longer time.

In terms of travelling time and cost the differences between Gatwick and
Stansted are likely to be pretty insignificant compared to the flight and
airport waiting times and flight costs if you are talking about central
London. One or other may give an easier journey from the airport to your
destination but it really does depend on exactly where you are going and
there probably isn't a huge amount in it in many cases.

If your destination is outside of the central London area it might be that
one or other airport will start to suggest itself more.

G.