So we finally hired a contractor to do the exterior paint and no surprise we can't get the job scheduled. So we're starting over. Anyway, we have decided on Sherwin Williams Duration exterior paint which is "self-priming" So do we still need a separate primer or not? Some contractors say yes, others no. Advise please.
As always, thanks so much for your help.

Repaint or new construction?

Re-paint

I personally would not use a primer for a re-paint, especially if they are saying it is self-priming. Maybe hit the bare spots, if any, with a coat then apply the finish coat.

Yes, go with what the manufacturer says and not just some contractor.

No separate primer needed.

My mum's a designer, she said the self-priming paint would work (she also said contractors aren't designers). But she suggested that if the original exterior colour is dark that you may want to prime with one coat if your colour is an expensive brand. This is to avoid a lot of coats of the expensive colour.