We are traveling from Positano to capri this June. We will be 2 adults and a child with luggage. Is the high speed ferry the best way to get there? I dont really want to drive to Naples and take the ferry from there and a private boat sounds like it will be excessively expensive. Have never done this so would love to hear thoughts or experiences. TYI

I'd take whichever ferry from Positano best suits my timeframe; YMMV.
For your options, see rome2rio.com and follow through the links it provides.

If you do decide to take the ferry/boat from Positano to Capri be sure to have your lodging arrange advance reservations for you. The demand is high and the earliest boat will be filled in advance. Many people end up disappointed when they have to wait until nearly noon for the next one! Schedules may have changed since I was there, but just make sure you reserve ahead for what you want.

It appears I can buy tickets on line for at least one of the ferries. Thank you!