Starcom MediaVest Group (SMG), a new entry on the list, which ranked 42, provides staff with an on-site GP twice a month, a physiotherapist monthly and subsidised beauty treatments.
SMG undertook the largest graduate training programme in its history in the past year, taking on 10 graduate trainees and making no redundancies.
Liz Nottingham, HR director at Starcom MediaVest Group said: "This recognition matters because it is all about our people and our culture which in turn lead to great work. We are doing the right things and this has been acknowledged by our people who experience SMG on a daily basis."
Leo Burnett was ranked at number 61 on the list. A total of 80% of Leo Burnett employees said they were proud to work for the company, according to the survey.
Marketing data companies Dunnhumby and Experian QAS also feature, at 57th and 59th respectively.
This year's list had fewer medium-sized ad agencies compared to last year, which saw Iris ranked 10th, AMV, 57th, BBH at 85th and DDB at 86th. Media agency MediaCom was placed 53rd.
Glue London, Brand Learning, Meteorite and Elvis all appeared on this year's Sunday Times 'Best Small Companies to Work for' list.