I'm slightly surprised at the negativity here. I agree with Simster that we're on course for parity at the halfway stage of the test, in which case I favour England. All of the bowlers are chipping in with wickets and most of the batsmen have had starts and shouldn't feel intimidated by the Bok bowling quartet.
AND we have Swann bowling in the 2nd innings, Harris is mediocre by comparison...
Sort of agree with this: I think it depends on how much our tail wags. If we're 40-odd behind on first innings, it could be a tough ask but if we get close to parity, I think England should be favourites. We have a spinner, SA don't.
Interesting to note that the top 4 in the batting averages are all SA-born (although I don't think it's fair to bracket Prior and Strauss with Pietersen and Trott - the former two were educated here, the latter two chose England as a career move and spent time qualifying as 'English').