I don't think SA are as strong a they're cracked up to be - yes they have AB and Amla, but they're very reliant on them, Du Plessis seems an unlikely no3 and Duminy has never quite nailed test cricket, and the rest of their top 7 are pretty inexperienced. Steyn's nearing the end and Morkel is a good test bowler rather than a huge threat. England have their own problems of course but should be a good contest.
Stokes needs to find a bit of consistency with the bat ideally, hopefully more runs from the top order will help with that, but with the ball he's been outstanding over the past year if you watch his spells rather than read the figures at the end of play. So many catches dropped off his bowling is Compton any good at second slip ha? Think Stokes is now good enough that he could be selected purely as a bowler, when the batting fires more often he'll win us a lot of tests.