3 days is not much time for the region.
I would not switch places for such a short stay, so vote for 1 place and commute to the other towns.
Normally Sorrento always wins logistically but in this case, Positano may work out better.
Capri takes a full day and is worthy of a full day ; Blue Grotto or not it still has enough to take up a full day and you will come back exhausted so don't try to fit in more.
There is a ferry from Sorrento or Positano. The Sorrento will run likely everyday in June, the Positano ferry I would say there is a small chance weather could affect it's running but should be ok.
Another perfect full day is combining Amalfi and Ravello into 1 day from Positano. Ferry to Amalfi, bus to Ravello, bus back from Amalfi to Positano would be what I would prefer.
As to your question regarding the bus: the bus ride is extremely scenic and usually an adreline rush, it is also much faster, more convenient and cheaper. So not saying avoid the ferry but rely on the bus and use the ferry as an alternative ; not the other way around.
Your 3rd day explore Positano, spend a couple of hours on the beach, then some time walking the streets (steps), visiting shops, etc...
Doesn't leave much time for Sorrento but given your timeframe it is the place I would skip ; alternatively you could base out of Sorrento and cut your time short in Positano.
There is not a more picturesque view than Positano in the entire Amalfi Coast. If you like the look of the vertical town, I know for me that look as in the Cinque Terre is almost the definition of a picture perfect town. Some views are more dramatic though, like those from up high in Ravello, Capri and Sorrento from the cliffs above looking out at the Bay of Naples.
Amalfi's views are not as picturesque, the better views in Amalfi are also from a little higher up.
Have stayed in both Sorrento and Positano and greatly prefer Positano though normally logistically and cost wise Sorrrento is most always better. There would not be any advantage to staying in Amalfi.