CIE is a little tough than EDEXCEL. EDEXCEL is hardly offered by any school in Pakistan. Most candidates who appear in EDEXCEL are private and are very few (maximum around 1000 in whole Pakistan while CIE candidates from Pakistan are more than 100 000 per session).
If you are planning to study in a Pakistani University, then I'll suggest you to go for CIE.
But if you are going to other Universities, then it doesn't matter whether you do EDEXCEL or CIE. Then all that matters is your grades. Because as far as acceptability goes, there is no distinction made by educational institutions at the tertiary (university/college) level. As long as the qualification is A-Levels, it does not make a material difference whether it's from CIE or Edexcel. Most universities will take the base structure of the qualification into consideration rather than the provider. So AQA, Edexcel, CIE are all equivalent when it comes to acceptance of their A-Levels. Moreover, since all the bodies running A-Levels and their curricula are administered and regulated using very similar standards (QCA, UK Department of Education), the choice is perhaps more on availability than value.