Ease of use, time to implement, user interface, and cost. Constant updates. Support team is also great.
The support we have received both working through problems, questions we had, as well as feature requests we've had has been outstanding. The system is easy to get started with.
The Canto team has been very supportive and have addressed every issue that we've brought up. Some of my early complaints were addressed in software updates, which regularly improve on features and functionality.
The main reason we selected Canto over a number of others we had studied was it's ease of use, price, and interface. We wanted something that looked clean and was easy to use, otherwise we'd be fighting not only our clients but our in-house team to use. No one likes working with ugly software. Canto hit it out of the park on all three categories.
Giving the ability of others in our marketing firm to search through our photo library (and video, branding images, etc) quickly and easily. We have also rolled out portals to a clients cutting the need for them to ask us to find photos and email them.