I have worked for firms where we used ProLaw and Compulaw, both of which I liked, but prefer Compulaw. The firm I am currently at (a small labor and employment law firm) uses Docket Enterprise, which my calendaring folks say is a behemoth and we will likely be moving away from it. I think the most important things for me in a calendaring platform are ease of use (how intuitive is it), its integration capabilities, and the ability to create custom rule sets (i.e., the State Personnel Board appeal rules, PERB rules, etc.). I also hear that My Case works well for small firms and sole practitioners.
Hope that helps?