It is the fifth consecutive year that VCCP has topped the table. The agency won the highest number of new accounts at 19, including First Utility and PDSA.
Martin Jones, a managing partner at AAR, called VCCP a "fantastic new-business machine".
Grey London was second place in the survey, picking up 13 accounts, while J Walter Thompson won 11.
Of the 25 new-business opportunities that VCCP had in 2015, the agency won five without a formal pitch.
Creature also picked up five accounts without a pitch.
Mcgarrybowen had a 100 per cent conversion rate, having pitched for and won five pieces of business.
Jones explained that this is "very unusual", adding that agencies with a conversion rate of above 75 per cent have done extraordinarily well.
These include Grey London at 75 per cent and Adam & Eve/DDB at 90 per cent (resulting in nine wins).
Jones also pointed out that the trend for agencies to be picky about what they pitch for was more apparent last year, with only two shops participating in ten or more "open" pitches.
He added: "Less is more when it comes to pitches. Agencies are being more selective and are spending more time to prepare for pitches."
Jones believes it is also increasingly rare for agencies to land business without a formal pitch. He said: "Historically, this has been the most cost-effective way of winning new accounts, but it is less prevalent than in previous years. Hats off to those that have been able to pull it off."
That said, Tesco moved its £110 million ad account from Wieden & Kennedy London to Bartle Bogle Hegarty without a pitch in January last year.