We currently use Highspot — before this we've used a number of CMS systems including Drive & Google Docs, Dropbox Paper, Percolate, and Docurated. We also evluated Guru and some others. We also use Confluence for internal documentation. No tool has been perfect — but we've seen good traction with Highspot.
The biggest challenge imho is on the usage side and getting solid adoption of the tool for all use cases (remixing, pitching, etc). I want good analytics and an understanding of how sales assets are used. The challenge is that there are still a lot of people keeping, storing, and creating presentations on their desktop. It makes measuring performance and impact harder — and also drives me a little crazy on marketing rights (logos/permissions/etc).
Also, if anyone has tips for how you measure and evolve marketing assets, I would love to talk. There is a lot of "I like this" and "I don't like that" or "we need this" but I would like to get a little more regimented to creating and optimizing assets.