Not knowledgeable enough to advise when to book.
Visited a few years back and looked at recently for a possible return visit in 2016 and found prices higher and more places booked than I expected / recalled ; I think the area is getting more and more known as a destination internationally.
Sorrento has a much different feel than the other towns.
We stayed 3 nights in Sorrento and 3 nights in Positano. Taking many day trips
In Sorrento you get more hotel for your money, larger common areas, nicer pools, amazing hotel views, etc...
Found it much more popular with tourists from UK. The town does not really have much charm and most of the hotels are a good walk from the town area. Town does have great shopping though and is best for taking the ferry to Capri.
Easy to catch the SITA bus to get into the other towns from there as well.
Capri is a must visit, so check the ferry as in the off season it does not run from Positano so you would need to catch from Sorrento. Easier to take a trip to Pompeii from here as well or reach Rome or Naples or course.
Positano has such a an amazing vibe and the town is so charming with the lack of cars and alleyways, we absolutely loved it.
Most of the tourists were from the US.
Much nicer than Sorrento as far as a place to stay other than your room likely won't have the same million dollar views or amazing pool and common areas and you will have paid more for less room for the priviledge of staying there.
You want to get out and walk all evening in Positano where Sorrento you want to retire to your cozy hotel balcony after dinner.
We rented a motor boat from the beach and was able to take that all the way down the coast which was cool, others took it to Capri but we were just there the day before.
I did not care much for the town of Amalfi to be honest. Wonderful for a day trip but would not stay there overnight.
The smaller towns like Priano are pretty and worth getting off the bus to visit but would get very bored very fast there.
Ravello is heaven, one of the most beautiful places I have ever seen. There are 2 villas there which I think you have to pay to enter but are must visits. I would love to stay in Ravello for a couple of nights.
Be careful with all of the places that list their location as a specific town but they are actually aways down the road, if you can't walk into town easy you really aren't staying in that town.
Would love to go back and if I did I would break up 2 nights each in Capri to experience the island overnight after the ferry tourists leave, 2 in Positano and 2 in Ravello.
We stayed in the Hotel Eden Roc in Positano and loved it there. Amazing breakfast, views from room balconies are incredible, has a pool and location great for the SITA bus.
In Sorrento we stayed at the Hotel Bel Air ; view from the room balcony was probably the most amazing view from hotel I have personally ever stayed at. Like most places in Sorrento was on a road outside of the main town on the cliffs above and built right into the Cliffside with a dream pool!