Out of these 2, I'd personally go for Reading. Considerably older university, slightly higher average entry grades for this subject (65% v 64%), research quality for the subject is only 2% lower at Reading (83% v 85%), To put in context, Reading's research quality for Psychology is just as good as Bristol, 2% higher than Durham, and 7% higher than Bath. And Reading still ranks above St Andrews on Edurank for Psychology.
For, graduate prospects overall as a university, Reading is currently rated 81%, Sussex 76%. For graduate prospects for Psychology, Reading 69%, Sussex 63%. Source: The Complete University Guide.
I've long felt that Reading is like Leicester - some great departments, traditional universities with often achievable grades, and the campus/es and accommodation are more loved than the city centres themselves.