As well as looking at upload and download speeds, Broadband Genie tested how well the dongles coped with common web activities such downloading podcasts and streaming audio and video using YouTube and Spotify.
T-Mobile came top in three out of the five categories; Best download speed, best upload speed and best coverage (joint winner with Virgin Media), as well as being named runner up in the best dongle software category.
On average, the T-Mobile dongle achieved download speed of 1.9Mbps, with some results registering as over 3Mbps. The average upload speed recorded by Broadband Genie was just over 1Mbps.
Last year's winner, Virgin Media, was named the overall runner up.
"Getting mobile broadband to work well on the move presents some real problems for providers, especially in more rural areas, but as we work towards establishing a universal minimum standard for UK broadband, these challenges need to be met," said Broadband Genie editor Chris Marling.
"Most of the ISPs showed no major progress from last year's tests, despite several putting up their 'up to' speed claims."
Ralf Pearson, senior propositions manager for mobile broadband at T-Mobile, said the network was "delighted" to be crowned overall winner.
"This is a thorough examination of relative mobile broadband capabilities, so for T-Mobile to come top is testament to the strength of the mobile broadband services we offer our customers," said Pearson.
This really shows that when customers use the service for browsing on the move that they can get a great experience that complements their home broadband.