Assuming 15-20 knots SE:
Saturday the low tide is at 2:30pm, so if you go to Shearwater you'll have a bit of a struggle to get back upwind at the end of the day (depending on ability/fin/wind). So Saturday is probably best at the train (end of Smith St motorway). Watch out for lots of boats, jetskis and the odd seaplane, and get there early to get a park.
Sunday there's racing at Manly... 'nuff said

You can't really tell what's going to happen more than 2 days out, certainly I wouldn't be counting on the forecast to tell you which place will have more wind, forecasts on all major sites were completely wrong last weekend. Not saying there's anything wrong with the forecast sites, just saying it's a tricky business, this forecasting lark