I could not disagree more with Jonathan.
As a trainee Sociology teacher, who studied a degree in Social Sciences at one of the top ten Universities in the country (as well as working within the admissions department of the University), I feel I am much more qualified to answer this question than Jonathan who doesn't have a clue!
Sociology GCSE will not be regarded as a poor choice by top universities. Of course, the subjects which you choose at GCSE are important, but what you take at A level will matter more. If you are planning to go down the Sociology, Psychology,History, Business or English route, Sociology will be looked upon favourably.
The GCSE Sociology is a fantastic introduction to Sociology. It is a varied and interesting course which covers a wide range of topics (such as the family, media, crime and inequality). Whilst some of the concepts can be complicated, the content is enjoyable and incredibly relevant to modern society. It is also a great foundation for A level, as it covers some of the same topics (but they are obviously looked at in more detail at A level).
I am of course biased but I would say go for Sociology!