Thomson Reuters topped the list—landing first in all three index measures: awareness, favorability and innovation.

Internally, Acritas brand researchers have tracked U.S. alternative legal industry players since 2013. During that time, awareness of the rivals to traditional law firms has grown. The company's findings show, for instance, that awareness of Axiom Legal Services has nearly tripled since 2013, according to Lizzy Duffy, an Acritas US vice president. Axiom came in second place on this year's published list.

To compile its rankings, Acritas researchers engaged in 276 interviews with respondents working for organizations with $1 billion or more in revenues, who have senior responsibility for buying legal services. Respondents were asked to “name organizations that provide legal services, excluding law firms, that first come to mind, along with those they most favored,” according to a statement Acritas issued with a release of the new rankings.

The other top five companies after Thomas Reuters and Axiom were LexisNexis, Deloitte Legal and PwC Legal.

U.S. multinationals increasingly turn to the Big Four accounting firms for alternative legal services in non-U.S. jurisdictions and also use them in the United States for work such as taxes, the Acritas researchers found.

“Dozens of different brands were mentioned in our study, ranging from technology platforms for research and information to outsourcing models delivering legal work. From the clients' perspective, one thing is clear: efficiency is king but quality won't be compromised and with an increasing choice of flexible solutions, it doesn't have to be,” Duffy said in a statement.

Last year, Acritas published its first global ranking of alternative legal service providers by brand. Thomson Reuters topped that list as well.