I don't think there is any difference between prepaid and postpaid reception is there?
I think the mobile reception varies from area to area. We are in Saheel and our reception is fine but I remember visiting a friend in Al Reem in the past and she had to put the phone outside on the windowsill to get any reception (that was a few years ago).
We have the basic Du Internet, landline and TV package and it is fine. We have a wireless router and all 4 of us can be on our computers at the same time with no problems. My kids download lots of music and my DH downloads movies and TV programmes with no issues.
HTH