basci question about queryset for retrieving top element

Hello!
I want to get just the top element of one queryset. SO I have
something as
qs=MyModel.objects.filter(...).order_by(..)

and then use qs[0] and check some value

I wonder now if i did the right thing or it is better to use .extra on
queryset.
Is the queryset object allocated for all objects, or is django/python
smarter than me and gets only the needed object?

Should I maybe do directly
topObj=MyModel.objects.filter(...).order_by(..)[0]

What is better?
Thanks
Nenad

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