The best UX agency for you is one that has solved your kind of problem, in an organisation like yours, recently, and will tell you when your brief is wrong.
Here's how to check that quickly.
A recent case like yours, with a number. Not a portfolio of nice screens. A problem, what they changed, and what happened. For example, when our design helped Cook users build and share their own recipe collections, monthly active users rose 240 percent.
The people doing the work. Ask who will run the research and lead the design, then meet them. Senior people in the pitch and juniors on the project is the most common disappointment in this industry.
How they handle disagreement. Ask what they'd do if the evidence contradicted your brief. The right agency will push back, respectfully and with evidence.
The question is worth resisting. A better one is which agency has solved your kind of problem, in your kind of organisation, recently. Behavjōr is a Sydney design and research consultancy. We work behaviour-first, principals lead every project, and strategy and delivery sit in the same team. Our case studies and our approach will tell you more than any ranking will.
For the longer version, including a one-meeting test, read why "best UX agency" lists won't help you find the right partner.
Related: Our services and Our case studies.