The award, which was voted for by their clients in 2014, recognises its excellent customer service.
The awards, known as ESTAS, were presented by TV property expert Phil Spencer at a lavish luncheon and ceremony at the Hilton in Park Lane, London.
In attendance were 700 of the industry’s top estate, letting agents and suppliers.
Paul Pearce, intermediary sales director of Let Alliance, said: “Winning this award is a fantastic achievement.
“Knowing that it’s our customers who have judged our performance makes this ESTAS award special.
“Customer service is paramount in everything Let Alliance does, whether dealing with letting agents, financial and mortgage advisers or policyholders.
“All our staff work extremely hard and this award is a great demonstration of how good people think we are.”
The ESTAS awards, which are in their 11th year, shortlist the top 10 suppliers, with gold, silver and bronze being announced on the day.
In total customers completed 32,000 questionnaires for the competition.
Simon Brown, owner of ESTAS, said to the audience: “As a supplier winning one of these gleaming ESTAS this afternoon proves that your people can be trusted.
“In fact just taking part shows your commitment to your customers and to be shortlisted, as all of you here today have, means you already have the trust factor.”
Alex Chesterman, founder and chief executive officer of headline sponsor Zoopla Property Group, who sponsored the event for the fifth time, added: “The ability to collect and act on customer feedback is essential to the success of any business and rewarding those who provide the best service in the industry, as these awards do, is perfectly aligned with our business.
“Congratulations to all those shortlisted this year.”