Principality achieved a customer score of 80%, with nine in ten customers saying they did not experience any problems with their mortgage, according to the latest survey conducted by Which?.
The building society gains five stars for flexibility of payments on its mortgage, and nearly all customers said they were satisfied with their mortgage.
First Direct and Nationwide both scored 77% to come in joint second. Virgin Money came fourth with a score of 76%, Coventry Building Society claimed fifth place with 75% and Skipton Building Society received a score of 73% to come sixth.
Kensington was bottom with a customer satisfaction score of just 56%. According to the survey, the lender received two stars on value for money and two-thirds of customers have paid the standard variable rate on their mortgage.
However, Which? highlighted that Kensington specialised in lending to people with bad credit ratings or complex circumstances, so its rates are higher due to the increased level of risk it takes on.
Accord Mortgages received the second-worst customer score of 61%, with one in seven of its customers being dissatisfied with their mortgage.
The survey of more than 3,500 mortgage customers looked at customer service, the mortgage application process and value for money.
Julie-Ann Haines, chief customer officer at Principality Building Society, said the team is very proud to be recognised by consumers and experts as the best mortgage lender in the UK for customer satisfaction.
She added: “We have made some significant improvements over the past two years that have improved the experience to our members. It is much quicker for customers to complete their mortgage applications thanks to simplifying processes, while we have also made investments to improve our online service to complement the amazing personal and tailored service our branch and telephone colleagues provide.
“It would be impossible to achieve such recognition without the fantastic work of all our colleagues who look after the best interests of our Members every day.”