Kensington Diana Exhibits advance purchase - which method gets me inside the quickest

Buying tickets ahead of time for Kensington Palace, dates are available for the Princess Diana exhibit but not enough time to be actually mailed. Which is faster: "If you choose 'Print at Home' , please print out all tickets individually and show at the point of entry, failure to do so will result in delayed entry. Please note we do not operate a fast track entry system, you will need to join the queue to enter the palace. At present we do not accept tickets on mobile devices. If you choose to ‘Collect on site’, the credit/debit card you pay with and confirmation email/voucher will need to be shown when collecting tickets from the Ticket Office before going to the gate. If you choose ‘Collect on site’, you will need to collect tickets from White Court". have seen other sites have kiosk where you could enter the confirmation and present the actual credit card at a machine and not have to wait in a ticket line for a person but this is not mentioned on the Kensington website and seems to be that you go to a manned ticket booth .Which method should I use? Do you have any experience or tips to share? Is Kensington and specifically the Diana exhibit worth it and the waiting times? Do you think there is a difference in number of crowds on a Friday afternoon vs Sunday vs a Monday?