There are a good number of boutique consulting firms and analyst firms offer this type of research articles. Gartner, Aberdeen, ARC advisory group(think these guys are already part of Gartner), IDC Research, VDC Research are some analyst firms. Consulting firms such as Tompkins, Envista are a couple of small size firms that specialize in this area, they typically help with WMS selection and sometimes also act as a third party integrator that helps with deploying the WMS, then of course there are the big consulting firms, Accenture, Deloitte, IBM Global, Cap Gemini etc.
Every CIO/SVP of Supply Chain/COO hire a trusted advisor type of consultant, typically the Tompkins, Envista type of guys take up that role and that is usually through relationship, either they got a personal referral or have worked together in the past. Then these trusted advisor consultants bring in their expertise and help the client company formulate an approach to vet the WMS vendor and help with vendor selection. These trusted advisor consultants help put a team together, then they also facilitate designing a high level WMS requirements by coming up with a simple WMS design that is a pretty close replica of what the real final design will look like. Then they ask the potential WMS vendors to do a proof of concept for that design. The WMS vendor that is able to closely mirror that in their proof of concept will be the one chosen and the project is awarded. Eventually these trusted advisor consultants also play the third party integrator role, meaning even after WMS selection they stay and make sure the processes are designed correctly, the WMS is tested thoroughly and ensure a complete deployment.
I would recommend reading some white papers in these trusted advisor type of consultants, that would give a good overview of what WMS is the best, again don't be surprised if the frequents answer to that question is "it depends", because there are so many factors that decide, What is the vertical?, What is the throughput volume? What is the technology preference, based on what they are running now? What is their ERP running currently on? How big is their shop?How many developers they have? etc