AutoCad is the most popular of CAD packages used by most offices around the globe and it is easy to find trained staff to manage AutoCad workstations.
As head of design for many years, I've the opportunity to try out various CAD softwares - specially ArchiCad, Microstation and Bricscad.
The most cost efficient package is Bricscad which is very compatible with AutoCad, but is bascially ment for 2D drafting, like Acad LT. This in fact is good enough for 80% of the work stations in a normal design office, as all would not be working on 3D objects. But then again one would need to send staff for a little bit of training. Still exchaning files over the net means having to convert drawings back to AutoCad so that the user at the other end who is not using your package can work on the same file.
The best option is to try out a trail version of various packages, which is normally supplied by the vendor and determine for yourself how well the software suites your goal. In my experience, due to lack of trained personnel, the costs to train people and the difficulty of sharing files with external offices let us to conclude that for the moment AutoCad satisfies our requirements. But with the development of the IT industry we never know.........